Yarn over(yo)
Yarn over, abbreviated yo, is one of the basic building blocks of most crochet stitches. To create different types of stitches, it may be used before or after the hook is inserted into the piece, or multiple times per stitch.
HOW TO YARN OVER (STEP-BY-STEP WITH PHOTOS)
Wrap the yarn from back to front over the hook (or hold the yarn still and maneuver the hook). This movement of the yarn over the hook is used over and over again in crochet and is usually called "yarn over", abbreviated as "yo".