Your SIM is attached to your User Guide. You will need to remove the appropriate sized SIM for your handset from the larger plastic surround and insert it into your phone.
Exactly how the SIM fits into your phone will depend on the phone you have, and you should consult your handset’s user guide for more information.
If your phone shows “Insert SIM”, “No SIM”, “SIM Error” or a similar message then your SIM may not have been inserted correctly.
Remove the SIM and try again. Make sure the SIM is the right way round, and that its metal contacts are clean.
If your SIM is correctly inserted but you are outside of a network coverage area then your phone will display a “No Service” or “No Network Coverage” message.