To practice editing, go to the sandbox and click the "Edit" tab. An editing window that contains the text for that page will be displayed. Type in something, or make changes to the text you'll find there. Then click the Save page button and see what the result looks like.
If you edit a page that people will read, you should follow two additional steps:
First, any time you edit a page, it is considered good etiquette (or "Wikiquette") to enter an explanation of your changes in the Edit summary box, which you'll find below the edit window. It's okay for your explanation to be quite short. For example, if you are making a spelling correction, you might just type "typo". Also, if the change you have made to a page is minor, such as correcting a spelling or grammar error, check the box "This is a minor edit" (this box is only available if you have logged in).
In the sandbox page, click the "Edit" tab again and write "Testing" in the Edit summary box.
Second, you should always use the Show preview button. After you've entered a change in the edit box for the sandbox, click the Show preview button instead of Save Page. This lets you see what the page will look like after your edit, before you actually save. We all make mistakes; this feature helps you catch them before other people see them. Using Show preview before saving also lets you try format changes and other edits without cluttering up the page history. Do not forget to save your edits after previewing, though!
Save the page
Done the edit summary? Previewed the page? Then you're ready for the final step: click the Save page button.
VisualEditor (VE) is a way to edit pages without needing to learn wikitext markup. It is only available to registered logged-in users if they opt-in, by changing your preferences. For instructions on using VisualEditor, see Wikipedia:VisualEditor/User guide. (Note: VisualEditor is in the beta testing stages and does not currently work with Internet Explorer).