I must say that double crochet is my favorite stitch. I work with it in all my crochet projects. Now I am using it for making a table rug. Also I used loads of double crochet stitches for making granny hexagons, my granny hexagon tutorial. Double crochet = treble crochet in UK terminology. Though I neither follow US nor UK crochet school, I use US "double crochet" as it corresponds Russian crochet terminology. I know there are many tutorials in the net however I wanted to make my own double crochet tutorial to link it to my projects. So here we go!
This is your initial loop, it can be a loop in the process of crocheting (like in the picture below) or a loop in the very beginning, when you have just made a chain of stitches.
Step 1. Slip on yarn.
The next double crochet (treble crochet) you will have to make in the next from a hook stitch.
Hope it was useful and please, give your suggestions on the improvement of tutorials :)
***Have a nice weekend!***