First off if you are not familiar with the provisional cast on here (http://www.knittingatknoon.com/ProvCaston.mpg
) is a pretty simple one from Knitting at Knoon.
After you have done the required 17 rounds, you should remove the stitches (a couple at a time) placing them on a second needle. Once you have all the stitches onto the second needle you should knit the top and bottom together with a third needle similar to a three needle bind off. http://www.knittinghelp.com/videos/casting-off
(Scroll down to the bottom for Amy's video demonstration). Only make sure the smooth "V" side of the stockinette is facing outward.