Chain 21.
Half double crochet 20.
I used my ballpen for this instead of a knitting needle. I guess chopsticks will do to. :D You need to have 20 loops inserted on the pen.
It should look like this once you have inserted 20 loops.
Take the first 4 loops.
On the first 4 loops, you yarn over and secure them with a single crochet, chain 2, this will serve as your first half double crochet. Then add three more half double crochet. therefore there should be 4 half double crochet in every 4 loops. There should be a total of 5 groups.
Keep on doing the same steps until you have 4 rows.
Add another row of 20 half double crochet.
Then finish it off with single crochet as edging for the 4 sides. This is the wrong side.
And this will how it looks like on the right side.