Activate iPhone
- Turn on and set up iPhone.
- Wake and unlock.
- Set up cellular service.
- Use Dual SIM.
- Connect to the internet.
- Apple ID and iCloud. Sign in with Apple ID. Use iCloud. Subscribe to iCloud+
- Find settings.
- Set up mail, contacts, and calendar accounts.
Turn on and set up iPhone - Apple Support (IN)
Please look at this --> If you can't activate your iPhone - Apple Support
Carrier Lock:- Request your iPhone’s original Carrier to unlock your iPhone and if they agree and do it, then you may know the further process here --> How to unlock your iPhone for use with a different carrier ...
If you are the owner or the owner has shared all information with you then, in order to open the Activation Lock:- read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support
If you have an unknown Apple ID on the App Store and Apple ID page. (See the pic below)
Learn how to remove a device from a previous owner's account.
If you are not the owner and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password with you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their Apple ID.