"HELP!" As you know, we bought this new 'puter last weekend, WELL.....a 'puter whiz I ain't

It came with a optical mouse, NOW....what the heck are the little buttons on either side of the mouse for???? I've yet to figure this one out, "What, ME read instructions?" "LOL!" I've never read a set of instructions in my life, I've always *figured* it out by *doing*, cept this one, it's got me stumped!
8) Dennis 8)