Securing my wireless network

Hello, i recently got an airport express station, hooked it up to my router and it worked right away. Right, here's my problem, i'm running two powerbooks, an acer laptop off the wireless network, and the router is connected to my pc. How do i make my wireless network secure from outside use?

Thanks

enable wep. go into the routers or airports setup options and enable wep and require a password to use the connection.

How do you get to the router settings? (I just got my powerbook and etc today so I'm so new to MAC )

Your Router Comes With An Ip Address In The Manual, Open Safari And Enter That Ip Address In The Url Field, Hit Enter, Itll Take You To The Router Setup.
Sorry About All Caps, Just Realized Caps Locks Was On.