The MyPage feature is similar to My Yahoo or iGoogle, or Netvibes, that kind of thing. It allows users to make personalized custom pages by choosing to add content to the MyPage from the catalog of available content. However nothing is in the catalog until you make it available on My Page. You can make existing site content available in the My Page catalog by marking it as "Available for My Page" in the feature instance settings. For example if you wanted to make you home page content available in my page you would visit the home page and click the settings near the title of the content on home page. In settings on the General tab you will see he checkbox for "Available for MyPage".
The documentation about MyPage is here:
on that page is a link to a Flash movie showing how to use it, but the feature itself does not use Flash nor Silverlight. It is based on ASP.NET WebParts and ajax that allows drag and drop. ASP.NET WebParts came out in 2005 as part of .NET 2.0 and I was kind of excited about it then so I built the MyPage feature, but it never really caught on in the ASP.NET world and today I think the MyPage feature is pretty lame. I had thought that a lot of third party webparts would become available and could plug in to the MyPage feature but that never happened. There are WebParts on the market for Sharepoint but they are not the same as ASP.NET webparts and as far as I know there are zero available add on WebParts for ASP.NET today.
Hope that helps,