As mentioned most bonuses come with wagering requirements, these must be fulfilled before your bonus is turned into real money you can withdraw or continue playing with, without any restrictions.
The wagering requirements will vary from casino to casino and depends on the type of bonus you get. You might get a match bonus and free spins with the same requirements, or one might be higher than the other.
If you get a 100% match bonus and deposit 20 $, the wagering requirement being x30, this means that you need to play your 20 $ bonus: 20 x 30 = 600
You need to play with the money you win with the bonus money until you have played for 600 $, whatever is left on your balance is then real money.
This might sound hard to complete, if you take into consideration that most online slots have an RTP percentage of 95-98%, you see that this is often very doable. It might take some time to fulfill the requirements as the max bet per spin is usually capped at 5 $.
Not all online slots will be available when working towards fulfilling the wagering requirements. Some casino games providers or certain slots might not pay towards the requirement. It is also worth taking note of the fact that most table games pay nothing or very little towards the wagering requirements.
Make that you as a new player read through all the terms and conditions that accompany your welcome bonus. This ensures that you don’t come across any surprises, you know the requirements, time you have to complete them and any restrictions.