hi, please help me, what can i do?

The phone is locked to a cellular carrier other than the one you are trying to use.

Only the carrier it is locked to can unlock it for use on other carriers.

Either return the phone for a refund, or contact the carrier it's locked to and find out if it can be unlocked.

To clarify the comment above.

You do NOT contact the carrier you are attempting to user (your carrier).

You contact the carrier the phone is locked to.

Only the carrier it is locked to can unlock it.

If you don't know who that is, ask whoever you got the phone from or call AppleCare and give them the serial number.

You get a sim card from the carrier the phone is locked to or request that the carrier unlock the phone.

Install a valid sim or contact the cellular provider it’s locked to and request they unlock it.

You contact your carrier and ask them to unlock the phone.

Use the Contact Support link at the top of this page.