WiFi is a wireless broadband connection that may or may not require a security password to access. You can connect to a public WiFi hotspot, such as in cafes, bars and other public places or just to your home broadband via a wireless router. The key advantages of using WiFi instead of the mobile network are speed and to avoid using valuable free data allocation. WiFi is normally free to use unless you are in a location which charges for a specific amount of time such as a hotel or an airport.
Not all phones have the capability to connect to WiFi so it is best to check your phone's compatibility before trying to connect. The process to connect to a WiFi network varies from phone to phone so check your manual, but in general you go to:
Menu > Settings > Networks or Connectivity > WiFi > Search for available networks
Please be aware that unsecured networks may not be safe to send confidential data over so, where possible, it is best to use a secure wireless network.