There are exactly two things you need in order to contribute to OpenWiki: something worth adding, and the Edit button.
That is the whole process. You do not need an account to do any of it.
Edits made without logging in are credited to Anonymous in the page history. The edit form has no field for a name.
Registering an account gives you a name that is yours. Usernames are unique: once Ada is taken, no one else can edit under it, so when a page history says Ada made a change, it means the person holding that account did. Accounts need a username and a password. No email address is collected, so a lost password cannot be recovered.
Anonymous edits appear in recent changes alongside the rest.
Start from Special:WantedPages, pick a red link, and write two or three paragraphs. A short, accurate, well-linked article is far more useful than a long unsourced one. Add {{Stub}} at the top if it is clearly incomplete, and finish with a category.
It goes live immediately. There is no approval queue: edits are published first and checked afterwards.
Three things happen around that:
A small number of pages are protected or use pending-changes review. These are applied to pages that attract repeated damage.
Other people will change what you wrote. This is not a rejection; it is how the encyclopedia gets better. If you disagree with a change, raise it on the page's discussion rather than simply changing it back.