How do you secure your router so that someone living next door is unable to use it? Or a nearby laptop.

Log in to the router, get out the manual and follow the directions for configuring/setting up the security options. You probably have WEP, WPA-PSK, and WPA2_PSK. The last one has the best security. You need to see which one your wireless adapter will handle. Whenever you do any configuration changes on your router you should be connected to the router by ethernet cable to do it.

Even if you have little or no technical knowledge, you can secure your wireless network in little time with these 5 simple tips:

• Secure your access point administration interface: The default passwords of most standard devices are already known to most hackers. So, when you set up your router through the web interface, change the default password and write it down somewhere safe.
• Stop broadcasting your SSID: Your wireless router continuously transmits your SSID (Service Set Identifier). While this is useful in an office where many people are going to connect to your network, at home this is certainly not needed. Turn SSID transmission off as soon as you can. Wireless LAN "sniffers" will still be able to detect your network, but other than that, your network will mostly be shrouded from outsiders.
• Use MAC address filtering: Turn on MAC address filtering on your wireless router configuration utility. By doing so, you can add the MAC addresses of all of your networking devices to the address pool of the router. This way, no one outside your home network will be able to access your network.
• Reduce the power of transmission: Reduce the power of your wireless transmitter to such a degree that the signal does not reach outside your home. This will keep most outsiders at bay.
• Disable remote administration tool: Your remote administration utility is seldom used. So, keeping it on exposes your network to outsiders. Turn it off for enhance your network security.