How to Knit on Circular Needles
First, cast on the number of stitches you want. Then (assuming you are using a circular needle--the kind with a flexible cable or tube), stretch out the stitches you just cast on so that they go all the way from point to point. Make sure they are not twisted around the needle (the cast on row will make a spiral around the cable at some point if they are twisted). Hold the needle so that the working yarn (that goes to the ball) is attached to the point that's in your right hand. Now, knit the first stitch from the point in your left hand (this was the first stitch that you cast on). Keep right on working stitches from the left point, sliding the knitting around the cable from time to time so that the knitting feeds from the right point, around the back, to the left point. Never turn back. If you want to make stockinette stitch, you just knit every round (what you see is what you get). If you want to make garter stitch, then alternately knit one round and purl one round.