A shared Space has two ways of talking. Boards are for anything with a subject that outlives the day. The room is for the rest.
Boards
A board holds threads. A thread has a title, a first message and replies under it, and it stays put, so somebody joining the Space in March can read what was decided in January without scrolling a chat.
Two boards are always there and cannot be deleted or reordered. The first is the notice board, and what it is called depends on the Space: a Household calls it Family Notices, a Team calls it Announcements. The second is Updates. Your own boards sit under those.
Starting a thread works the same way from either door, the board itself or the composer, so there is only ever one thing to learn.
Replies
A reply belongs to a message, one level deep, in the same channel. There are no threads inside threads and no reply that quietly goes to one person: a reply reaches everybody who can see the channel, through the same read as everything else.
On a desktop, replies fold under an "N replies" door and open beside the thread. On a phone they stay inline where you can see them.
The room
The room is the fast half. Type, press Enter, done. Formatting is a row above the composer rather than something you memorise, and a web address becomes a link while everything else stays text, deliberately, so nothing anybody types can render as markup on somebody else's screen.
Pinning
Pinning a message flags that line. It never makes a copy, so a pinned message that gets edited is the edited one, and unpinning takes nothing away.
Who sees what
Everything here belongs to the Space it was written in. Your Private Space is shared with nobody, including whoever administers the household. Sharing is decided per Space and you pick which.
In a Team with boards owned by departments, somebody outside a department does not see that board's threads or the tasks hanging off them. That is enforced on the server rather than by hiding buttons.
Reporting something
Any member, post, thread or line in the room can be reported from where it sits, under a short list of reasons. A report about child safety goes to a senior review with a 24-hour clock on it.