Bethany gave a good reply. To do stockinette in the round you never need to purl, you just knit, knit, knit and the st st happens.
There are several ways to join in the round, but basically when you have all the stitches divided around the needles instead of turning at the beginning like you normally do to begin knitting your first row in flat knitting, you just keep going in the same direction. You don’t have to do anything special really to join (although there are things that can be done) just start knitting it into a circle.
Lately I have been joining by casting on an extra stitch, then taking that last stitch cast on and moving it to the first needle (so it is at the beginning), knit the extra stitch and what was the first stitch together. Makes a nice join.