Click the Start button.
Try the Hotter and Colder buttons.
Click and Drag inside the moving atoms to rotate your view (there's a bug in this too -- rotation left&right works, but up/down is slightly broken).
Enter a different number of particles and click Start again. (more than 200 can be sluggish, but its your machine ;-).
This applet is a simplistic simulation of the movement of the "atoms" of an idealized chemical. The physics of the interaction are not really right (the atoms should be much harder, and have less long range attraction than what I've currently got, etc). But it's fun to watch, and gives some inkling of what's going on with molecules in various phases.
(Copyright 1999 Joe Hopfield, Plasmid.net - joehopfield@plasmid.net).