When you create or edit any page on this (or any) wiki, it is considered good etiquette to enter a brief explanation of your changes in the Edit summary box between the edit window and the Save and Preview buttons.
If you've made a complex collection of edits, please take a moment to reflect on what's significant about what you just did. Your summary might be "Added new content and wiki-linked some pages." Or it might be "removed outdated information" or "reorganized per today's meeting." It also might be pretty simple, like "created page" or "several minor fixes." But keep in mind, almost anything is better than nothing!
Your summary can be quite short; for example if you just enter "typo", people will know you made a spelling correction.
In addition, if the change you have made to the page is minor, such as correcting a spelling or grammar error, you may wish to check the box "This is a minor edit".
You can include wiki links in the edit summary if you like, between [[double brackets]]; they will appear in the page history as functioning links!
Along with diffs, edit summaries make it easier for other editors to understand what you're doing -- and that understanding is a basic ingredient of friendly and productive collaboration!
Note, there is a setting in your Preferences screen that will make the site remind you if you try to save a page without an edit summary.