Securing a wireless network

Hi. We just got a new wireless router and it's all connected and we can access the internet from it, which is great, but we want to set up the network so we can secure it. The wizard says to plug in a usb into the router or input the data manually into the router, but there is no usb port on the router, and I can't see any other way to input the encryption into it. Our router is an ASUS AM 604g. Please help me to set up the network and secure it so that our data is safe and people can't steal our bandwidth. Thanks.