How does MediaWiki work?

You probably know Wikipedia, the free encyclopedia, and may possibly be a little bit confused by similar, but different, words such as Wiki, Wikimedia or MediaWiki.

To avoid a possible confusion between the words you may first want to read the article about the names where the differences are explained. 

General Overview
MediaWiki is free server-based software which is licensed under the GNU General Public License (GPL). It's designed to be run on a large server farm for a website that gets millions of hits per day. MediaWiki is an extremely powerful, scalable software and a feature-rich wiki implementation, that uses PHP to process and display data stored in a database, such as MySQL.

Pages use MediaWiki's wikitext format, so that users without knowledge of XHTML or CSS can edit them easily.

When a user submits an edit to a page, MediaWiki writes it to the database, but without deleting the previous versions of the page, thus allowing easy reverts in case of vandalism or spamming. MediaWiki can manage image and multimedia files, too, which are stored in the filesystem. For large wikis with lots of users, MediaWiki supports caching and can be easily coupled with Squid proxy server software. 

Try out Wikitext
Yes, you can easily modify pages and you can (temporarily) publish dummy sentences, and you can even (temporarily) completely destroy a page in a wiki. You don't need to have any programming skills to do this.

We suggest you exercise yourself within our sandbox. Please isolate your testing there, though: the admins might not take too kindly to your mischief otherwise.

You can also look up the with basic formatting commands.