Taking pictures

I'm not a photographer (obviously) I'm a snapshot kinda girl. Which is why I like this project. It gets me thinking and paying attention to how I take pictures. Sometime I'd love to take a photography class.

My sister in law got us a camera several years ago for Christmas and I loved it, it was simple and easy to use. A cannon powershot, so when that one broke (ok, by me dropping it) I got the newer version. This ones a couple of years old now, a powershot A570. It's not a bad camera. But all my pictures all seem to be coming out grainy lately. Now, this very well could be because I don't take care of my camera. It often travels in my purse, unprotected. Or a coat pocket. Or my husbands pants pocket.

Does anyone know what's causing the grainy-ness? Is it my failure to take care of it properly? Are my settings screwy (I do mess around with settings not having a clue what I'm doing) or is it just basic user malfunction, do I just suck at taking pictures?

Help?