Turning Chains (tch)
At the beginning of a pattern worked in rows, you chain a certain number and then begin your pattern stitches into the foundation chain.
At the end of a row, a pattern will say to chain a number of stitches and turn.
Turning chains make your first stitch the height of the remaining stitches on your row.
Here are the typically suggested turning chains for the basic stitches, as well as where to place your hook on the foundation chain. You may find you need fewer or more chains to get to the proper height.
Note: Turning chain counts as a stitch in all but ss and sc, which means you work into the tch as your last stitch, unless otherwise specified in your pattern.
The exception might be the half-double crochet. Some people prefer not to count the tch as a stitch for a hdc. In that case, you would go into the 2nd ch from hk on the foundation chain, and after turning, go into the first stitch of the row. Whatever your choice, be consistent.