Dear Tgr, Welcome to MediaWiki.org!
Yes, Welcome! This site is dedicated to the documentation of the MediaWiki software, the software behind many wikis, including that of Wikipedia and the Wikimedia Foundation projects.
Please, take a look at the following pages. They might prove useful to you as a newcomer here:
If you have any questions, please ask me on my talk page. Once again, welcome, and I hope you quickly feel comfortable here, and find this site a beneficial documentation of the MediaWiki software.