To edit, you must start by with log in.
If you are a user with modify rights, you can edit your page with the Edit link on top.
This opens the page as textarea. Edit it using the Syntax and save it with the Modify button.
To create a new page, create a link on an existing page for it, then click on the link and you get the message: This page does not exist. If you have create rights, you can click on the Create link to create the page.
If multiple languages are enabled, there are Edit links for all languages. There is also an Edit Multi link that allows you to edit all language versions of a page in one window.
Leave a short comment when you make changes to a page so that you remember the reason of the changes in the revision history.
Use the History link to see old revisions of the page. You can click on each revision to see the diff to the current revision and eventually revert it.
If you have the respective rights, there are also the following buttons below the text area:
Protect or Unprotect to lock a visible page.
Rename to rename the page.
Delete or Undelete to remove a page.