Turning chain
When we have done the first row, we have the needle at the outer border of the row. When you now turn the work you have to lift the crochet height by a stitch or more. Just crochet one (or more) chains. Turning chains will be used mostly when you crochet in rows. The border of the work will be even and the stitch count stays the same.
As more height a row has as more chain you have to crochet.
For a row with single crochet you crochet one turning chain
For a row with half double crochet you crochet two turning chains
For a row of double crochet you need to crochet three turning chains.