The two sides generally look an awful lot alike, and if you're working back and forth in rows, it's really hard to tell. Usually, though, the tops of your stitches will have one side with a clear place to put your hook - it looks like a series of loops or circles across the top - and this is considered the right side. The other side doesn't have those circles. Once you do a piece that has you work in flat circles, you can more easily see the difference.
I like to do filet crochet, which has little blocks across it. This kind of crochet pretty much doesn't have a front or a back. On the other hand, a circular doily does. Or, if you do a piece with popcorn stitches - that has a front and a back.