To edit pages on this site, click on the Edit button, either at the bottom of the page or on the right of the wikidot menu bar at the top. This will open an editor.
You will then have a lock on the page when no one else can edit it. After 15 minutes of inactivity the lock automatically goes off. If you input text your 15 minutes will be extended.
When you have finished editing, click the Save button at the bottom if you want to save your changes, otherwise Cancel.
For a more detailed account of editing, see the Wikidot documentation on Editing Pages. This should suffice for most purposes, but if you have further questions a wealth of information is available on the Wikidot Documentation and Community pages.