No, you cannot use free spins on all the slots at a casino or even on multiple games. Most of the time, the casino will give you free spins for just one slot. Even if you are getting 5 free spins per day for 5 days, you can use them in the same slot. Some casinos will give you free spins you can use on multiple games, but they are pre-selected as well. Other casinos can give you free spins to use on multiple slots but are developed by just one software developer. This is ideal to promote a slot game.