|Now you'll see a small dialog box. Here you should enter a brief summary of your actions (in the box that says "Describe what you changed"); this is the edit summary. The number at the bottom right of the box, which initially is 255, shows how many more characters you are able to enter into that box.
You can also mark your edit as minor, and you can add (or not add) the page to your Watchlist.
If you click the "Review your changes" button (recommended), you will see a page that Wikipedia calls a diff. This shows, in wikitext format, the differences between the previous version of the page and what the page will be after you save it (if you don't change anything more).
When you're on the "diff" page, if the differences (changes) look good, you should click "Return to save form" to continue the page save process. If, instead, you want to make further edits to the page, you should click the "^" in the upper right corner.
Finally, after you've entered the edit summary, checked (or not) the minor page edit and page watch checkboxes, and reviewed (or not) your changes, you should click the "Save page" button to complete your edit.
(If for some reason, at any point, you decide you want to return to editing, click the "^" in the upper right corner of the dialog box.)