Free chip and match bonus offers for playing online slots will always have a wagering requirement, also known as a playthrough requirement. This is the total amount of wagers that you need to make on slots only before you can withdraw the real cash that you have won. The wagering requirement is usually stated as a multiple of the free money that you received, and your progress toward meeting the requirement is often easily available to you within the online casino; if not, then you will want to keep track of your wagers so that as soon as you meet the slots wagering requirement, you can see if you have won and withdraw your slot machine winnings.
Timed offers have a limit on how long you can play with the free money that you are given. Once the time is up and you have winnings, the winnings are transferred to your bonus account. The winnings in your bonus account are subject to a wagering requirement as described in the above paragraph.
For each site listed at Free Slots 360, the wagering requirement on slots only for your free money will be clearly stated.
(Of course, if you run out of money (or time, for timed offers) before you meet the wagering requirement, then you can't withdraw anything! In this case, just go to the next online casino, claim their offer, and try again!)