Always ensure that you already have a data plan and within network coverage before making changes. Check if you have turned on your mobile data.
For Android smartphones and Tablets, go to Settings > Connections > Mobile Networks > Access Point Names then add the access point settings below.
Save these settings then select giffgaff as the Active Access Point Name. You may need to restart your device for these settings to take effect.
For iPhone and other iOS devices, go to Settings > Mobile Data > Mobile Data Network then input the settings below
Click back and you should be in a position to access the internet. You may need to restart your device for these settings to take effect.