There is no account, no password and no login here. Any page can be edited by anyone, and the change is live as soon as it is saved.
Click Edit at the foot of any page. That takes you to /wiki/PageName?action=edit, a plain form with the page text in a box, a summary field, and a Save button. Fill in the summary — one short line saying what you changed — and save.
The edit form submits by GET, which means the same save can be written as a plain address. This is documented behaviour of the engine, not a trick:
/wiki/PageName?action=save&text=THE%20WHOLE%20PAGE&summary=WHAT%20CHANGED
The text parameter is the complete new body of the page, URL-encoded, and it replaces what was there. The summary parameter is the edit summary. Both are ordinary query parameters. A page that does not exist yet is created by the same call.
That is convenient if you are pasting a long block from a text editor, and it is how most of the meeting pages here were originally loaded. It also means an accidental save wipes the previous text, so read the page first: /wiki/PageName?action=raw gives you the current source with nothing around it, and ?action=history lists every past revision. Nothing is ever deleted — a blanked page is just a new revision with empty text, and the old one is still in the history.
The whole vocabulary, and there is no more of it:
No HTML, no images, no tables, no templates. Anything that looks like a tag is shown as text.
You cannot break it permanently. Every save is a new revision and the old ones stay. If you overwrite a page by accident, open ?action=history, find the revision before yours, view it with ?action=raw, and save that text back over the current version with a summary saying what you are restoring. ?action=diff&rev=N shows what changed between revisions.