Circular needles are used for knitting socks to pile all of the stitches on one needle. Use circular needles with tips from a knitting teacher in this free video on yarn crafts.
When you're using two circular needles to knit your socks, you're also going to use the long tail cast on method, and you're going to cast on all the stitches onto one needle. Then you're going to slide those stitches, so that your working yarn is at one end, and your stitches are at the other. And you're going to take your second needle, and you're going to take half the stitches off one needle, and put them onto the other. Then you're going to take them off, putting your needle in from right to left, and you'll take off half the stitches, and transfer them onto the other needle. And when you've got those all on the needle, you're going to slide those stitches, both of them, to the other end, so that your working yarn is at the tip. And again, you're going to have to make sure that all your stitches are facing the same direction, so that your stitches aren't going to get twisted when you join them. I'm going to take the other end of this first needle, I'm going to put it in the first stitch, I'm going to take the yarn from the back needle, and knit it into that stitch, and that will connect them in the round.