How can i activate my sim

Contact your service provider and ask to activate your sim. Have your iPhone handy as the provider rep will ask you for your IMEI number from Settings > General > About. They will likely want the pin number that you established with them for that phone service too.

Are you getting an error message?

Did you try the general troubleshooting for no data network?

If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support