0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
In our numbering system, we talk about Place Value. We have the 1's place, the 10's place, the 100's place, etc. For example, the number 143 has a 1 in the 100's place, a 4 in the 10's place, and a 3 in the 1's place. The value of 143 is 1 hundred + 4 tens + 3 ones.
In the hexadecimal numbering system, you also have place value. But instead of 1's, 10's, and 100's, it has 1's, 16's, 256's, etc. Where do these numbers come from? Well, 100 is 10^2, and 10 is 10^1, and 1 is 10^0. The same is true for hexadecimal. 256 is 16^2, and 16 is 16^1, and 1 is 16^0. And so on, for even larger numbers.
So how do you convert from hexadecimal to our system? You take the value of the digit (0 through F) and multiply it times its place value (the 1's, the 16's, etc.) Take for example, 36B. That's 3*256 + 6*16 + B (where B is 11, remember?) So that's 768 + 96 + 11, or 875.