Very, very few people have modems (per se) these days. Almost everyone has a wireless router (which incorporates a modem). So the chances are that what you've already got is sufficient for one end of the set-up. (If you're unsure what you've actually got, take a look at it and tell us the make a model number).
All modern laptops have wi-fi connectivity built into them. (Other computers might need a wireless adapter, which plugs into a USB port).
So (assuming that you've already got a router, rather than a basic modem, together with a laptop) you don't need any other equipment. You simply need to know the router's wi-fi password and you can connect the two together. (The password might be on a label attached to the router or in documentation from your ISP. If not, once you've told us the make & model of your router we can tell you how to find it out or reset it).