It feels like being taken out of a life and given an existence. You're locked away from everything and everyone you knew and introduced to a whole new way of existing.
Jail is NOT a place where you'll make friends. You'll make a lot of acquaintances, but you will learn quickly to not trust them enough to be true friends.
This isn't from personal experience it's just from what I've gathered through watching prison and jail documentaries and reading on the internet about jails and prisons.