The shortest stitch in crochet and used for joining, the slip stitch is important, yet easy to learn. In some patterns this may simply be referred to as a "join". These pictures are an example of the slip stitch being used to join "in the round".
Start with your specified number of chains. Make sure your chain is not twisted before you join.
Insert your hook into desired stitch, this case being the farthest from the hook.
Yarn over, pull through both loops on hook.
Practice slip stitching in the round, or simply along a row. It is better for your tension to be slightly loose. If you make the stitch too tight you'll never get the hook back in it too make another stitch.