WAP stands for Wireless Application Protocol which isn't really relevant in this case.
What you are probably looking for is WEP (Wireless Equivalent Privacy), which involves the use of an encryption key generated via a password or passphrase. Each machine you want to allow access will need this access key in their wireless configuration in order to log on - Any machines trying to access it without permission will be unable to log on.
Alternatively you can set up MAC address filtering. Each network device (network card and so forth) has a unique MAC address by which it can be identified. By adding the MAC addresses of each network device you want to allow access to your routers configuration, you can again bar access to any unauthorised persons.
Both methods are very difficult to circumnavigate so it all depends on which will be the easiest for you to implement. If you are unlikely to introduce new systems to your network, either method is suitable. If you are likely to have friends or colleagues round that wish to log on to your network, WEP access is probably more suitable as you can keep a copy of the encryption key handy rather than having to log on to your router and add each new device's MAC address.
Both security measures can be implemented via the routers control panel. Simply log on to your router using the details given to you on your instruction leaflet and look for something along the lines of "Security" or "WEP Encryption". Follow the on screen instructions and it should lead you through generating an encryption key and adding it to each machines wireless configuration.