Can I find a friends iPhone through my iphone

Yes, open the Find My app, scroll to the bottom and tap Help a Friend.

Your friend can also log in to https://icloud.com/find and do it themselves.

No, you do not understand correctly. You can let your friend use Find My with their Apple ID and password.

If I understand your answer correctly, the Find My App can help anyone locate anyone else, not just friends. That's disturbing. I really hope I misunderstood your answer.