I think you can protect your WiFi by securing it by a passphrase/password in modem settings. If some one tries to connect to your WiFi then it asks for passphrase/password. It is called "Security Enabled Network".
For your laptop also, you can put password to open it. Make different user accounts like one for administrative use, another one for browsing and general use.
This what I know as a lay user.
you can configure your access point according your own requirement even in every access point /modem security options are available. Simply login in your modem console and choose security options 32bit/64bit/128bit according your need and provide pass keys for same.
