You can use Wi-Fi as an alternative to the mobile network when establishing an internet connection. This way your phone doesn't use mobile data.
Press Wireless & networks.
Press the indicator next to "Wi-Fi" to turn on the function.
Press the required Wi-Fi network.
Key in the password for the Wi-Fi network and press CONNECT.
Slide your finger upwards starting from the bottom of the screen to return to the home screen.