craftgrrl | Crochet help needed! (Reply)

Okay, so I'm working on my next project (work it, baby! work it!), and I've run into something which confuses me greatly. Here's what the pattern reads:

Sk sl st, sl st in each of next 2 sts, sc in each of next 2 sts

I know what that reads as. Skip the first stitch, then slip stitch into the next loop. I've got that. But then it suggests doing another two slip stitches, followed by two single crochets. If it's just to the next loop, what's the difference between a single crochet and a slip stitch? I've never been able to figure that out, and I don't exactly want to mess up my project over something like this.

Help? Anyone? Please?