Beautiful and pure, Belldandy is what most of us would expect a Goddess to be. Working in the Goddess Help Office to help grant wishes because she enjoys watching us mortals smile and be happy, Belldandy is already one of the best there is in Heaven (Asgaard in Norse Mythology). Summoned by Keiichi and bound to stay by his side by a Contract (and a promise in the OVA), Belldandy is one of the main characters of the series.

Working in the domain of the Present, Belldandy recieves her energy from Yggdrasil via her Goddess Markings, like any other Goddess/God on Earth. However, in need, Belldandy can draw her energy from Nature as Yggdrasil only provides a limited amount of energy to her as a protective measure against energy abuse. On Earth however, Belldandy shares Keiichi's interests in all sorts of vehicles and merrily learns many other things during her stay with him.

As a Goddess, Belldandy believes in the best of everyone and even demonesses like Mara are seen by her as having her own good points and potential goodness. Belldandy also believes that people must try their very best through their own power, for she knows that the rewards for such efforts are great and that she hopes others will understand this. She almost never gets angry and seems to forgive others at a moment's notice. Also, being the being of purity she is, she doesn't understand some of the negative human emotions that strike her from time to time, such as jealousy. And such as she is, Belldandy is never  truly/knowingly selfish will always encourage others to do their best, although she doesn't seem to know how to deal with her own problems sometimes.

Bearing the secret knowledge bestowed upon Goddesses that reach first class, Belldandy also carries an incredible burden upon her with such knowledge. Apparently she is only able to reveal certain aspects of such information, and everything else is considered classified and top secret and cannot be revealed, enforced by a bond of silence. Of course, some of what she knows are simply lessons in life which apply to everyone, Immortal or not. Take heed, fans! ^_^

As a Goddess too, Belldandy is a perpetual source of happiness in the world. Following the Conservation Law of Happiness, mentioned by Urd, Belldandy ignores the normal rules of the law and constantly brings more happiness into the human world, thus replacing the unhappiness in the world with happiness. However, as she is bonded to Keiichi with a contract, it appears all misfortune/unhappiness strikes Keiichi should she ever give more happiness to others than she can make up for with her presence.

While most of us wouldn't expect a Goddess like Belldandy to ever bother herself with mundane things such as housework and cooking, Belldandy does happily go around doing such things for Keiichi. Some people might find this perfectly normal, but some might not. One theory is that as a Goddess and being such a positive thinker, Belldandy is entitled to eternal life and as such can take her time to enjoy the little things in life, such as housework. Another is that her love for Keiichi is enough reason for her to like it.

However, being a Goddess doesn't mean Belldandy is perfect. Of course, we all know she likes everyone and is always happy and pure, but she is intensely emotional. While it isn't a hinderance, it does occasionally build up a negative image about her being a crybaby. (see the Top Ten Anime Babes & Anti-Babes listing on the Turnpike's General Links to see what I mean)
Her positive attitude also makes her seem airheaded or ignorant of her surroundings from time to time, although she is probably anything but that at any time. Also, Belldandy is still learning new things and spells, which in time will mean her attempts at something new might fail. Some people seem to expect too much out of her just because she's a First Class Goddess.

But all in all, we all love that sweet, caring, hardworking, and determined Belldandy, don't we?
(You jealous types don't count.)

Observational Notes on Belldandy's Goddess designation in relation to the Real World : Goddess of the Present.
Note : Reading of the manga up to at least book 14 is required to understand some of the terms used here.

The Present" being "now", what you are reading is considered "the Present" and as even as you read this word alone, it is becoming "the Past". The "Present" is defined as whatever is going on at the moment, no matter what you yourself may be doing, it is also the "Present". You "exist" in the "Present" but also in the "Future" and have "existed" in the "Past" (See Urd's Profile) because you are making the "Present" happen by your very "existence". You create and exist in the "Future" because the "Present" cannot exist without a "Future" to constantly create it, the "Present" is affected by the "Future" because what you are planning to do will become the "Present". You also exist in the "Past" because the "Past" is simply what has already happened in the "Present" and you have already "existed" in the "Present".

"Ladder Tunnel Theory" :
The "Present" is eternal, a "ladder" shaped passage in which one passes through on one side only every single moment of their existence, yet never notices a change in their position, like standing still in space with a paint can and watching a neverending tunnel move before you, allowing you to paint the tunnel from your spot in it alone before going on to the next bit. It is the time in which you have the opportunity to change your surroundings before going on to the next portion of the passage and leaving the completed piece behind as the "Past". However, sometimes the "painted portion" might take the loop in the "ladder" and return again, as a possible "Future" or as the chance to amend a "Past", to which you can paint the tunnel again or leave it to the other "painters" in the tunnel to deal with. Remember, you don't exist alone in the "Present", although your paint supply is unlimited, the "Present" being diverse as it is.

Belldandy's designation as Goddess of the Present has its own special meaning.
The Present is comprised of everything the is happening even now, no matter where you are, and is what makes up the Past. It is also defined by the Future. The Present cannot exist without both the Past and the Future, and Belldandy is like that. Being the loving and infinitely patient (well, almost.) middle sister, she embraces both the Past and Future equally and unconditionally, and loves things the way they are, even though some rough times in the Present may occur as a result of the Past. (Cue Urd's "help".) However, the Present is nothing it can't handle by itself (Belldandy's Goddess powers), and even though it relies on the Future to make it what it is, the Present always takes precedence over how it defines the Future. (The Present is thus more influential than the Future being what it is.)
Take the conflict between Skuld and Urd for example. The Present is the great mediator between the two, and serves as a bridge to smoothen out the flow between the future into itself and then to the past. Along the way, it can be said that things may change by the time it becomes the Past, which is what Belldandy does when it concerns Urd, and often affects the future, as in the lessons Belldandy teaches Skuld which eventually become Skuld's own values in "time". She smoothens things out in the Present so that things may become better, both for the Future and for the Past by creating potential in the Future which is then passed down to the Past.. (see Skuld's Profile) And, being the Present, the values Belldandy passes down to Skuld, the Future, are all of Mankind's current virtues of which are eternal, and will perpetuate themselves into the Future.
Also, Belldandy is the important link between the Past and Future, as without her, there would be no such thing as the concept of time. Take the Lord of Terror incident for example. If the Present had not arrived to Keiichi, the Past would not have followed thereafter and the incident would never happen, thus the Future "possibility" would never have come. However, as the Present was "there", the Past naturally had to "follow", as does the Future, and the "Future" possibility for the Lord of Terror to appear was thus writ.
Think of it this way : Belldandy is the only Goddess of Time to know that Urd is also the Lord of Terror's first form. Only her presence as the Present can actually cause the release of the Lord of Terror to occur. Skuld need not know because it might never happen and thus she would never need to prepare for that future. Urd also need not know because since it might never happen, it would not have happened and the Past would never have recorded it.
So it's mutual. All timelines must exist with each other or the concept of time as we know it is.... well, nil. The Present is every little bit as complex as any of the other definitions of time.