You sign in with email or Google and pick a username. Friends and groups are the everyday chat. The vault keeps files out of the shared gallery. App lock, hidden chats, a decoy PIN, and disappearing messages are there when the phone is not only yours.
Random chat is optional. It stays off in the app until you turn it on. The website can start a text-only chat with a name, and that chat can move into the account when you claim it.