There are two basic ways of knitting, and different patterns will have you do it different ways. The first way is “Flat.” This means that you’re working in rows, going back and forth, making a piece that is… wait for it… flat. If you’re making a garment, knitting flat means that you’ll have seams to sew up at the end (unless you’re working on a cardigan). Not everything is a garment, though, and therefore requires knitting flat – such as a washcloth. It would be silly to have a tubular washcloth, so you knit them flat.
Knitting in the round, just like knitting flat, is exactly what it sounds like. You connect the first stitch to the last one and knit around and around in circles, creating a tube of fabric. For clothing, this is ideal because you don’t have to worry about sewing the flat pieces together at the end to create the tube you need.
There are lots of tutorials around on how to join your stitches to start working in the round, so if you’re interested in that method (which I highly recommend; it’s much easier in the long run than knitting flat), it will be easy to find one of those. YouTube can be your best friend 🙂