Wikipedia:Tutorial (historical)/Editing
Editing pages
We'll start with the most basic Wiki feature of all: Edit this page. With the exception of a few protected pages, every wiki page has a link at the top that says "edit." This link lets you do exactly what it says; edit the page you're looking at. Sites such as these where anyone can edit anything are known as wikis.
Try it! In a new window, open this page's sandbox, and then click the "edit this page" link (Caution: NOT the "edit this page" button above). You'll see the source code for that page. Write something pithy or amusing, or just say hello. Then save it and see what you've done. There is more detail at Wikipedia:How to edit a page. You might want to open this in a new window, too, so you can carry on with the tutorial.
Whenever you want to experiment without worry, you can always do it in the Wikipedia: Sandbox. It's a "safe area" of sorts.
Show preview
If you've written in your edit and want to see what it looks like click the Show preview button.
Minor changes
If you are logged in as a registered user, you can mark an edit as minor by checking the appropriate box before you save. This is used to show others that your edit is not something substantive. There's no strict guideline on when to do this, but certainly spelling corrections and minor format changes like adding a space or a wikilink are considered minor edits. In other words, changing the presentation is generally minor, but changing the content is not. When in doubt, don't mark the box. For a more detailed discussion, see Wikipedia:Minor edit.
Edit summary
Before you hit Save, it's considered good practice to enter a very brief summary of your changes in the Edit summary box between the edit window and the Save and Preview buttons. It can be quite terse; for example if you just enter "typo", people will know you made a minor spelling or punctuation correction, or some other small change.
When you're done playing around in the sandbox, you can continue to the Formatting section of the tutorial.