I start cello lessons on Saturday, and i played the guitar for a little while and hated it beyond belief. My question is this: for cello, do I play one string per note or to I have to play more than one to get the sound, also do I ever have to play more than one note at a time?

You can play however many strings you want at a time. 90% of the time you will play on one string at a time. The cello bridge is curved,(hint-hint).

This person on TV was playing the cello for fun added with comedy, and he played I dunno, 3, 4, 5 strings at a time (might be dangerous, ripping bow?) and it sounded really cool cause he was imitating a bagpipe!

Cellos have only four strings.