The treble (or triple) crochet stitch is about three times the height of a single crochet stitch. (It is called a double-triple or double-treble crochet stitch in England and several Commonwealth countries and is abbreviated d tr c, dtr, or 4-c.) In American notation, it is abbreviated tc or tr c or tr or 3-c. The photo at the right is from the American Thread Company booklet and shows both the front and back of the stitch. NexStitch has a video.
(The caption on the picture is for the double treble crochet st -- discussed later.)
This st and the other two sts discussed here are used mainly in lace edgings or doilies, etc and in Irish lace. They're fairly thin with definite space between the sts. They can be used in combination with the sc and dc sts to form shells.
Again, one starts with a single loop on the hook (and ends with a single loop on the hook). The difference is how many yo's to make. For the single crochet st, there was no yo before placing the hook through the top of a st in the previous row (or into a ch sp). For a dc, there was a single yo. For a tr c, there are 2 yo's.
Step 1. Yarn over (yo) twice. That is, wrap the thread around the hook twice (from the back over the hook to the front). There are 3 loops on the hook.
Step 2. With the yarn in back, put the hook through the top of the desired st -- or whatever (as you did for a single crochet st), yo, and draw the thread through. There are now 4 loops on the hook.
Step 3. Yarn over and draw the thread through 2 loops on the hook. There are now 3 loops on the hook. (The pic shows the yo part of this step.)
Step 4. Yarn over and draw the thread through 2 loops on the hook. There are now 2 loops on the hook.
Step 5. Yarn over and draw the thread through 2 loops. There is now only 1 loop on the hook, and the treble crochet is complete.
One might ask oneself what would happen if one made 3 instead of 2 yo's to start out. The answer is that one would have a double treble crochet st -- shown in the pic at the right -- abbreviated dtr or d tr c or 4-c. (It is called a triple treble crochet st in England.) Here is a link to the video at NexStitch. This st is about 4 times the height of a sc. It is not used very often even in lace.
The picture at the right is of the double treble crochet st.
Similarly, one could do 4 yo's to start out. The result is a triple treble crochet st (or treble treble crochet st or tr tr c or trtr or 5-c). NexStitch has a video. (I assume it would be called a double treble treble crochet st in England.) It's about 5 times the height of a sc.