Charts are the visual representation of the stitches in a crochet pattern. They are used in addition to or in place of a written pattern to describe a pattern stitch. Crochet has a system of symbols adopted by the Crochet Yarn Council and have become the industry standard. Each one of the symbols signifies one stitch in the pattern. Stitch symbols are arranged how they will appear in the finished work.
Watch this informative video from Bernat Yarns to learn all about how to read a crochet chart.