Every poker bonus comes with terms and conditions, and wagering requirements.
Most poker sites give you player points (PPs) in exchange for paying house fees that serve to track your bonus status (and other things).
The wagering requirements of a bonus could look like this:
For every dollar in rake you pay, you get five player points.
For every 25 PPS you collect, you get a reward worth 1$ in return.
For the whole $1000 to be transferred into your account as bonus money, you will have to to pay $2500 in rake within 60days.
So basically, all that a bonus does is giving you a discount on the rake you pay.