Q: actiovation lock

you don't.

It's mean to be a theft deterrent system, so there is no way for the users to circumvent the activation lock. It can only be 'disarmed' so to speak, by entering the original apple ID and password used to set up the device.

if you bought it from someone, get your money back, or get them to give you the apple ID and password to unlock it.

Have the previous owner do this:

Turn off Find My iPhone Activation Lock - Apple Support

Otherwise it is not usable by you