"Why do I chain 2 at the beginning of the row?"
==> Because you're working in hdc (half double crochet) (using American stitch terminology).
If you were working in single crochet (sc), the turning chain would be 1 ch st at the beginning of the row.
hdc = 2 ch sts at beginning of row
dc = 3 ch sts at beginning of row
tr = 4 ch sts at beginning of row
This way, the first complete stitch of the row isn't squashed or misshapen. There's room for it to be fully executed.
(Sorry, the last couple of weeks have been completely crazy....)