Thread:Project:Support desk/Starter questions about MediaWiki/reply

MediaWiki uses wikitext. See Help:Editing to learn how to use it.

There's also limited support for HTML. You can add JavaScript and HTML as you please, although JS cannot be directly embedded in wikitext for security reasons.

For the rest of your points:
 * By default, MediaWiki will use favicon.ico in your website root as the favicon. If you'd like to use an image from another location, modify appropriately. (Manual:LocalSettings.php explains how to customize your settings.)
 * Custom domain support will depend on your hosting provider. We do have documentation on how to create a wiki family though.
 * The MediaWiki software itself is free. If you're using a third-party hosting provider, they might charge. Be sure to ask them about the costs.
 * Every page on the wiki has its own talk page where discussions can take place. Or you can hold discussions wherever you like. That's up to you to decide. There are also extensions available to enhance the forum capabilities. The threaded discussion happening right here is made possible by Extension:LiquidThreads; you may be interested in that.
 * By default MediaWiki is completely ad-free. Advertisements can be added though, and if you're using a third-party hosting provider they might add advertisements. That's another thing you'd have to ask your provider about.