Chain Stitch
the starting chain almost every pattern is built on, plus turning chains between rows

The chain stitch is the first stitch most people learn, and the one every other crochet stitch depends on. A row of chains becomes the foundation you work your first row into, and a short chain at the start of each new row (a turning chain) brings your hook up to the height of the next stitch.
There's no US/UK split on this one. Chain stitch is "ch" in both systems, one of the few terms that doesn't shift between them.
How to work it
- Start with a slip knot on your hook.
- Yarn over (wrap the working yarn over the hook from back to front).
- Pull the yarn through the loop already on your hook. That's one chain.
- Repeat step 2 and 3 for each additional chain, keeping the loop on your hook loose enough to work into later.
Count your chains by looking at the V-shaped stitches on the front of the chain, not the loop currently on your hook. That loop isn't a finished chain yet.
When to use it
Use a starting chain to set the width of a project before your first row, and a turning chain at the start of every row after that. How many turning chains you need depends on the stitch: 1 for single crochet, 2 for half double crochet, 3 for double crochet.