When working crochet in rows or round, you will need to work a specific number of extra chains at the beginning of each row or round. The extra chains are needed to bring the hook up to the correct height for the particular stitch you will be working next. When the work is turned at the end of the straight row, the extra chains are called a turning chain, and when they are worked at the beginning of a round, they are called a starting chain.
The turning or starting chain is usually counted as the first stitch of the row, except when working single crochet (sc) where the single turning chain is ignored.
For example, ch 3 (counts as 1 dc) at the beginning of a row or round means that the turning or starting chain contains three chains stitches and these are counted as the equivalent of one double crochet stitch (dc). A chain may be longer than the number required for the stitch and in that case, counts as one stitch plus a number of chains.
For example, ch 5 (counts as 1 dc, ch2) means that the chain is the equivalent of one double crochet stitch plus two chain stitches.
At the end of the row or round, the final stitch is usually worked into the turning or starting chain worked on the previous row or round. The final stitch may be worked into the top chain of the turning or starting chain or into another specified stitch of the chain.
For example, 1 dc into 3rd of ch 5 means that the final stitch is a double crochet stitch (dc) and is worked into the 3rd stitch of the turning or starting chain.
Here are the numbers needed to make a turn for each stitch
Single Crochet Stitch (sc) - 1 chain to turn
Half Double Crochet Stitch (hdc) - 2 chains to turn
Double Crochet Stitch (dc) - 3 chains to turn
Treble Crochet Stitch (tr) - 4 chains to turn