Mac AirPort Question

[Gemini Cricket]

Does anyone on the board who is good with computer shenanigans know how I can turn my unsecured wireless network connection to a secured wireless network connection?

I have a AirPort Extreme white dealie that helps me hook up to the internets. I can't figure out how to make it secure so that my entire building doesn't clog up my intenet surfing with their internet surfing.

When I look at "available wireless network connections" I see other wireless customers out there with secured connections. I want to be one of them.