Just make sure that the wireless adapter on your laptop is turned on - there's usually a small switch on the front or side edge.
The computer will detect a wireless router that is in range, and you'll see a notification in the system tray at the bottom right of your screen. Click on it, and select your router. Your laptop will connect automatically, and will ask you for the authentication key that you set up on the router when you configured it.
Once you are connected you can access the internet, but if you want both computers to be able to see each others files you'll need to run the Windows networking wizard.