Signing up for their player's clubs will get you some free stuff, even if you never play any of the table games or their slots. That's the most free stuff you'll ever get from any casino, beyond that it's going to cost you.
Yes, you can play online slots for real money at licensed casinos in states with legal online casino gambling. These sites offer a wide range of options where players can bet and win real money. These winnings can then be withdrawn from the casino through various banking methods.