In order to stop unwanted users accessing your connection (important for security issues as much as not wanting them freeloading) you need to enable your security settings. It can be slightly different depending on the equipment (I've never used the Netgear unit you mentioned). If the paperwork that came with the unit doesn't explain how to secure the connection then maybe you can find the details for the specific model online.
Lots of info available on AAM by searching "wireless" and "security".