Casting on and joining on double pointed needles

To cast on DPNS, you will divide the number of cast on stitches evenly between 3 or 4 needles (pics show 3 needles as they are for mittens, and for mittens 3 DPNs are easier to work with that 4 because there is such a small number of stitches). Cast stitches on, then lay flat to make sure that the cast on row isn't twisted before joining (see pic).

Using a 4th (the "working needle"), insert it into the first stitch on needle 3, and knit that stitch (the yarn will be coming from the last stitch on needle 1, and once the stitch is worked, the work will be joined) Be sure to pull the first few stitches tighter than you normally would to keep the join snug and avoid the long stretch of yarn that comes with a loose join. (See pic)

Once the round is joined, you will simply work each needle as you come to it, around and around. To avoid the dreaded DPN "ladder", it is wise to rearrange the stitches on the needles every few rounds. I do this by knitting 2 extra stitches from the next needle every few rounds. This helps to move the stress points so that you won't get a visible ladder. If you do this, be sure to mark the beginning of your round before you rearrange the stitches, otherwise you won't know where the round begins!