What is worth doing on my first day with the POS?

Four things, in this order. Add your people under Settings, then The POS, so every sale carries a name. Pair one device and sell one real item on it. Open a shift with the change that is actually in the drawer. Close it at night, count, and read the Z report before you go home. That one loop teaches more than any manual, and every step of it is in POS and the counter in the docs.