if you are a continental knitter, when you have cast your stitches onto the circular needle, move the so they are evenly spread along the entire length tip to tip.
now, in your left hand hold the needle (tip) which has the tail yarn on (assuming you have don a long tail cast on) and in the right hand hold the needle (yip) which has the working yarn coming from it.
hold the working yarn in the left hand as normal making sure it passes behind the tip of the left needle, now knit your stitches as normal (including the tail yarn if you wish for a few stitches)
TADA!! you have joined your work and it is now in one big loop.
If you keep knitting round and round you get stockinette, ecause you are not turning the work as you would on straight needles. for arter you must knit one round then purl the next round then knit and so on. - thi is where stitch markers come in sefull so you know where the start of he round is!