Pretty much covered the basics, but to sum up, the ideas behind both:
Single side feeding - Use only one breast for each feed, switching to the next breast for the next feed. The idea is that if the baby stays on one side for the whole feed, he'll be sure to get the fatty milk (hind milk) at the end of the feed and not run the risk of getting too much foremilk and less fat, if you take him off too soon and switch sides. During growth spurts, you may want to offer the second breast anyway, though.
Double side feeding - Empty one breast, then offer the second breast at every feed. For the subsequent feed, start with the opposite breast first (the one you ended the last feed with). The idea with this is that both breasts are stimulated each feed, which can help with supply if that's a concern, you won't feel as lopsided, and baby may eat more (depending again on your supply). Also helpful if baby is sleepy - switching sides can wake them up because the flow picks up a bit!
For both, watch for the long suck-swallows that indicate baby is really eating and not just comfort sucking, and use breast compression when he slows down to get him going again and make sure you really empty the breast.
Let me know if you have more questions! HTH!