There is no account and no phone number, so adding someone works differently from what you are used to: you give them a code, once. This page walks through that and through the few settings worth understanding.
The first time you open the app it generates your identity and stores it encrypted on the phone. Nothing is sent anywhere and nothing is asked of you — there is nobody to register with.
The list starts empty. Everything else happens from My identity, at the top right.
An invitation is a code you give to one specific person. You give it a name — that name stays on your phone and never travels inside the code — and the app uses it to know who is writing the first time they do.
Each invitation works once. As soon as the person it was for has used it, anyone else presenting the same code is refused. That is why there is one per contact instead of a single code you hand around.
The code is bigger than a normal QR, because it carries the keys your contact needs to start an encrypted conversation with nobody in the middle. So it is split into four codes that rotate on screen: the other phone collects all four and puts them back together. Just keep the camera pointed until it completes.
If you would rather send it through another app, Copy as text gives you the same invitation as text.
Bear in mind what the code contains: your Tor address. Anyone who sees it can reach you, so show it only to the person it is for.
Your identity has a verification fingerprint: a row of digits. Your contact has one too, and the app shows you theirs in the chat. Read them out loud to each other, or compare them over some other channel.
If they match, nobody intercepted the introduction. This is the one thing the app cannot do for you, and it takes ten seconds.
The three values are covered up in this screenshot on purpose: they identify a specific phone, and this page is public.
Under each message you sent there is a state, and it means something precise because there is no server keeping your messages:
A message that stays queued does not mean anything is broken: it means they are offline. There is no inbox in the sky to leave it in.
The app is free and has no ads. The donation screen shows an address and, next to it, a short fingerprint.
Compare that fingerprint with the one on this site before sending anything. If someone rebuilt the app with their own address, that is how you find out. It is the same gesture as verifying a contact.
On by default. The app sends packets with no content, the same size and encrypted just like real ones, so that somebody watching your connection cannot tell whether you are having a conversation. It costs roughly 1 GB a month of mobile data, which is why the switch exists — and why the cost is written next to it.
If you turn it off, turning it back on the day you have something to hide is exactly the pattern that gives you away. It is worth leaving on from the start.
Setting a PIN means the encryption key needs two halves: your PIN and a secret held by the phone. Neither is enough on its own, so a copy of your data is useless to anyone without you. There is no recovery. Nobody can reset it for you, and that is the point.
With a PIN set, the app also asks for it again after a minute in the background, so that someone who picks up your unlocked phone cannot simply open it. That is a lock on the screen, not on the vault: the keys stay in memory so the app can keep receiving messages while your phone is locked. It stops somebody holding your phone, not somebody with root access on it.
Off by default, because it also blocks the screenshots you want to take, and the app cannot know which case is yours. Turned on, Android refuses screenshots and screen recordings, and replaces the app's preview in the recent apps list with a blank screen.