...and pull it through only 2 of the loops on your hook.
You'll end up with 3 loops left on the hook.
...and pull it through the next 2 loops on the hook.
You'll be left with 2 loops still remaining on the crochet hook.
Wrap the yarn over the crochet hook again...
...and pull it through the remaining two loops on your hook.
Here's how the completed treble crochet stitch looks. Notice that you are down to having only one loop remaining on your hook -- your "active loop."
You'll keep repeating those steps, over and over again, to make one complete treble crochet stitch in each of the chain stitches in your starting chain.
A Row of Treble Crochet Stitches
When you've crocheted across the entire row, here's how the completed row of treble crochet stitches might look.
Crochet Your Turning Chain
The next step is to work your turning chain. The turning chain for a treble crochet stitch is usually 4 stitches, meaning that you will work 4 chain stitches in between each of your rows of treble crochet stitch.
This number of chains isn't set in stone; it's simply a suggested number of chain stitches that works well for a majority of crocheters under ordinary circumstances. There might be plenty of reasons why you'd want to work a longer or shorter turning chain, and you should feel free to do so if you like.