1. Setup a default mobile data configuration settings. Go to Settings > configuration, and select your network operator.
  2. Confirm with your network operator that you have an active mobile data subscription (access to internet) on your SIM card.
  3. Enable the mobile data connection on your phone. Go to Settings > connectivity > mobile data and switch mobile data to On (check that your data roaming is activated when you are not in your home network).

If the above steps do not help, insert your SIM card in another device and retry. If it works in another device, contact your network operator for Internet settings reconfiguration.