Use this join to add a new color when beginning a row or round; it will give your work a nice smooth finish.
Begin by placing a slip knot on your hook (a), bring your yarn over the hook two times, insert the hook in the stitch where you what to add the treble crochet, yarn over and pull up a loop (b), yarn over and pull through two loops on the hook twice, yarn over and pull through remaining two loops on hook (c).
Treble Crochet Join (tr join)