Written information in Aurbis is physical. Books and letters have authors, holders, languages, and provenance. They can be carried, read, lost, stolen, and misunderstood by characters who do not have the right literacy or language proficiency.
Speech is fast and local. Writing is slower, durable, and valuable. That is why scribes are a profession path rather than decoration.
How it works
Writing happens at a desk. /scribe opens it, and from there you write a new book, letter or scroll, or edit one you wrote earlier. Writing costs one Roll of Paper and needs Speech 10.
What you finish is a real item. It goes into your pack as a book and opens in Skyrim's own book interface, so a written work can be carried, handed over, stored in a chest, stolen, or buried with its author. A writing that never got made into an item can be torn up at the desk by the number shown there. Once it is a real item, the only way to be rid of it is to be rid of the item.
Documents are written in the tongue you were speaking, and they are rendered for each reader against that reader's proficiency in it. A reader who is out of their depth is not told that they failed. They are given the text as their character understood it, which may be wrong in ways they cannot see. A letter can be intercepted and still not understood, a foreign document can need a translator, and a scribe who reads and writes clearly is valuable because they move information across those barriers.
Tamrielic is the common tongue and always works. The other nine tongues need proficiency before your character can use them.
Maps are drawn and scribed at the same desk (see Maps of Skyrim), and letters travel between holds through the post offices (see Aurbis Post and the Hold Notice Boards).
Commands (/help scribe)
/scribe opens the writing desk to write a new book, letter or scroll, or edit one you wrote.
/scribe write is the same desk, spelled out.
/scribe list lists your writings by title and number, and which of them never got made into a real item.
/scribe discard 3 tears up one that never got made, by the number shown at the desk.
Languages (/help language)
The tongues themselves are their own system now. See The Tongues of Tamriel for the nine tongues besides Tamrielic, the proficiency a character needs to speak one, and how a written work is corrupted for a reader who is out of their depth.
The older /scribe write <book|letter> <title> | <body>, /scribe inspect and /scribe read forms are gone. The desk replaced them.