To work a slip stitch,
A slip stitch is the shortest of all the crochet stitches and is mainly used for joining rounds, making seams and for carrying the hook and yarn from one place to another neatly.
1. Insert the hook from front to back into your required stitch.
2. Yarn over the hook.
3. Pull the yarn through the work and the loop on the hook. One loop now remains on the hook and one slip stitch is completed.
Repeat until you reach your desired position.