As mentioned, there are a lot different features on the app and these are easy to access and understand.
Registration is most commonly via a link to your facebook account.
However, this is not obligatory and you can just sign in with a private e-mail account.
Most of the services on the platform are free, including crucially, the ability to chat with whoever you want.
However there is a coin system and a subscription option that enable add on permissions or functions.