Wrap the yarn round the crochet hook (a)

Insert the hook under the top loop of the second chain stitch and wrap the yarn round the hook (b)

Pull the yarn through the chain loop only leaving 3 loops on your hook. Wrap the yarn round the hook and pull through all 3 loops (c)

Wrap the yarn round the crochet hook and insert the hook under the top loop of the third chain stitch (a)

Wrap the yarn round the hook and pull the yarn through the chain loop only, leaving 3 loops on your hook (b)

Wrap the yarn round the hook again and pull through the first 2 loops only (c)

Wrap the yarn round the hook again and pull through the last 2 loops (d)

You’ve now made a treble crochet. Continue working tr into the next and all the following chains to end of the row.

Double Treble crochet (dtr)- Wrap the yarn twice around the hook and continue as explained for tr (a)
After (c) pull thread through two sts again, before (d)