how do i unlock my iphone?

Your newly purchased iPhone is carrier locked. To unlock this form of a lock you will need to contact the carrier that the iPhone is locked to. Contact that carrier and ask them about the requirements to get the iPhone unlocked.

Axel F.

You will need to contact the cell service provider it is locked with and ask what their unlock policy is and if you qualify. Check Settings > General > About to see what Network it is locked with or call AppleCare and tell them you just want to know what cell service provider it is locked with.

This indicates that this phone is still locked to another carrier. That also means that the original owner (I'm assuming that this is a used phone) did not properly restore the phone to its original "out-of-the-box" condition.

At this point, you need to contact them to get this resolved; otherwise, this phone will be useless to you.