You can limit your data usage by turning off mobile data. You'll then not be able to access the internet using the mobile network. You can still use Wi-Fi even though mobile data is turned off.
Step 1 of 4
Find "Mobile Data"
Tap Settings.
Step 2 of 4
Find "Mobile Data"
Tap Mobile Data.
Step 3 of 4
Turn mobile data on or off
Tap the indicator next to "Mobile Data" to turn the function on or off.