I know that I can only use 2 cards from my hand.
If, for example, I get TT2Q in my hand and the board is QA347, then do I have:
QQAT7 or TTAQ7?
I already have Pocket 10's. Don't I have to play them?
Yes, exactly as you said you have to use 2 cards from your hand, apart from that it works exactly as NLHE in the sense of hand strength.
The reason you don't need have to play with pocket 10s is QQ beats TT.
Let's change your board to explain how each street your hand may change. So you have the same hand TT2Q.
The flop is still the same of QA3.
On the flop your hand is now QQAT3.
Let's say the turn comes the same. QA34. Your hand now is QQAT4.
Let's say the river comes and now the board is QA34T. Your hand will now be TTTA4. You take the two cards from your hand that gives your the strong end hand.