Look at your sample. Is it a single crystal (or collection of crystals all made of the same thing?)
Yes: You don't have a rock, you have a mineral.
No: You have a rock.
More help with this question:
A rock is an aggregate of one or more types of minerals which may be present as crystals or grains. If your specimen is a single (or collection of) crystals, all made up of the same thing, you're probably looking at some kind of mineral. If it’s metal, you could be in luck, it might be a native element like gold or silver, or more likely, it's one of the sulphide minerals like pyrite - often known as fool’s gold. Alternatively, there's a very small outside chance it's part of a meteorite!