When you enter or leave a country, they will always check your passport. This is to check that you are allowed to be there, and that you are not a known criminal or terrorist.

Inside your passport you must have a photo. Someone who knows you well must sign that photo, to say that it is definitely you.

When you have a passport photo taken, you get copies, so that they can be kept on file.

Every ten years or so, you need to renew your passport, and get a new photo taken.