Dig out the literature for your router and see how to get into the router's user setup screens. In there you can review or renew the wireless security password.
Start up netbook -- see instructions manual for netbook for how to turn on wireless adapter. Go to Windows Networking - select wireless connection, scan for router's signal select that and apply password.
If you have difficulties go back to step 1 and turn of wireless security in the router until you get a reliable connection.