It says demon starts with 4 TP, do you actualy refresh those every round or no?
No, it just means you have 4 already right at the beginning of the scenario. Any more TP you need to earn by putting dice on the board.
Also imagine you use 2 TP and keep 2, can you use those 2 later or they are all consumed used or no?
You keep them for later rounds.
So you could for instance spend a few rounds just gathering TP, and then spawn a whole bunch of monsters in one go.