In order to secure your wireless network, you should follow both of the steps below. Keep in mind that any security is better than no security. The steps below do not depend on each other, so it is ok to do one or the other, but you really should do both.
To secure your network please view our Wireless guide for this router. It will assist you in turning on wireless security, defining a password for your wireless network, and making your wireless network mostly invisible to your neighbors.
To prevent others from connecting to your network take a look at our Filter guide for your router. A filter is a way of limiting which computers can connect to your wireless network. They are an effective additional layer of security that will help keep prying eyes out of your documents.