Umm...I have wi-fi in my house. How do I secure it?
read the manual that came with it, it should pretty much spell out all the steps.
You do have a couple of options:
1) Use WPA encryption if you have the choice. WEP is trivial to break
2) when specifying the strength choose 128 bit instead of 64
3) Optionally, restrict it to the MAC address of the network card(s) in your own computer(s), that way the router won't talk to other machines than those particular ones.