Look up the spec sheet / user manual for the MBP. It will tell you the type of video port it has, e.g. DVI. The same for the monitor. Let's say its VGA. In this "for instance" case, you would need a DVI to VGA cable.
So look up specs of both devices. If the MBP has a mini- something port, you would have to buy an adapter.
These type of cables are readily available. (Every monitor I ever bought actually included one or even two types of cables.) You can buy them at places like Best Buy or even the computer parts store around the corner.
By the way, this part of the Discussions is for Snow Leopard related questions. In other words your post is in the wrong place.