Only MagicBand+ work at DLR (if you are buying them at the park, that’s all they sell so don’t worry about that).
You do have to charge them. Bring an extra battery pack and it will charge in a few hours in your bag or backpack. It comes with a short charging cord. They use a proprietary cord, but if you ever need a replacement, they are pretty cheap. (Under $10, last I looked.)
If you do not want the lights or haptics on your first day, it will work to scan into rides and with the Photopass locations (ride photos are not integrated with MB+) even if you do not charge the band right away. It does need to be charged enough to pair though.
They come with instructions which were pretty easy. Pretty sure there’s also videos on
YouTube if you’re getting them before your trip. If you are planning to get them in the park, the cashier can walk you through pairing, as long as it’s not too busy. If the shop is too busy, take them to a blue guest experience umbrella, they’ll have you connected lickety-split.