Access Point Name (APN) is the way that your Global Packet Radio Service (GPRS) data-enabled cell phone accesses your carrier's data services.

Try to call your carrier's customer service from a different phone.

Tell them that you need to configure network access on the phone into which you just inserted the activated SIM.

Tell the carrier the brand and model of phone.

The carrier's customer service will help you get to the network settings on the phone and tell you the APN and any required user names, passwords, or other custom settings required by the carrier.