Hi, new to biking and all of the terminology, but I've been trying to read up.

Anyway, bought a new bike from Dick's Sporting Goods. It's a cheap bike, as I am on a budget. But it looked good enough for the occasional use I was going to put it to. Its a Diamondback road bike, with three gears in the front and 8 in the rear (making it a 24 speed?).

Anyway, the front gear will not change. I notice there are two screws that can be tightened or loosened above the silver thing that puts the chain into the different gears (is that called the cage?). I've been messing with them and can get it to upshift, but then not downshift...and vice versa. Sometimes it would shift, but then I can tell the chain is hitting that silver piece as evidenced by a clanking sound.

When I bought it, I got NO manual, and the lazy clerk only inflated the tires and checked the breaks. I don't know if he is supposed to check the gears or not, but he didn't.

I only bought it yesterday and will probably bring it back, as I called and they told me to bring it in so they can check on it.

Sorry for some newbness. Just looking for some answers if anyone can help. Thanks in advance!

edit, here is a pic of those screws:


In case its hard to tell, those screws are 90 degees to the length of the bike horizontally. That is the side view of the rear tire.