Many patterns call for joining the chain when working in the round and the slip stitch is used for the join. If you are starting with a flat piece then your next step will be single crochet.
This cute pig pattern is from a 1943 booklet from the Spool Cotton Company entitled Crochet Your Victory Barnyard. There are also patterns for a girl and boy in addition to all the other barnyard animals. Since polyfill wasn’t around in the 1940s the the patterns call for cotton batting and all are crocheted with [...]