Originally Posted by Giles
It should be as simple as placing the condom over the end of your penis, the right way around (it'll be pretty obvious), then slowly rolling it down the length of your shaft. Make sure you leave a bit of a gap at the end though. If you're wondering what to do about your foreskin then that's really up to you - some uncircumcised guys pull it back and then put the condom on and others leave it forward with the condom on. It doesn't really matter either way, your personal preference.
I believe the penis is supposed to be erect before putting it on. The foreskin should be retracted before putting the condom on. (I think a bare glans is supposed to prevent ripping when the foreskin does slide back.)
Keep in mind that it's always best to try it a few times without a girl, so when you get that girl, you know what to do and don't keep her waiting.