Type !wiki in the game's chat (any tab). The server answers you alone with your player number and a code that lasts ten minutes.
Press Log in at the top of this wiki, enter both. Tick “stay logged in” and you will not need a new code for a month.
A number: on any data table, click a cell in the suggested or note column, type, save. The server's own cells are not yours to change.
Text: press Edit this page - everything under “Notes by players” is yours. The part above it is rewritten by the sync.
A picture: the media manager (the picture icon in the editor) uploads into the screens folder. Your own screenshots of this game only.
Log out everywhere: !wiki logout in the game.
The wiki's syntax is DokuWiki's: bold, italic, a link, '' * a list''. The toolbar does it for you.