This video shows how the yarn is positioned for stitches in crochet when both the yarn and the hook are held in the same hand. This is for right handed crocheters. (Sorry it's a little blurry.)
by Sikhte Raho
by Interweave Craft
by Crochet Together
by KNITTING & FOOD CRAFT
by Happy Toy Time
by SEI Crafts
by Stitch More