how do I hook up a new window sensor?

One of my window sensors fell out when opening window and came apart at the wiring. I bought a new sensor and want to know how to hook up and when I do hook it up will it then protect me. this zone has three windows linked to it and we've had to bypass that zone when we set the system. Also the security monitoring company wants to charge over $100 just to come out to look at it, so I wanted to fix it myself. Thanks