These websites can be used to either share files with friends and family on the web, or to have a place on the web, where you can get to your files from anywhere.
You can have some music on Mediafire, and then play it anywhere you want, or have videos on Tinypic or Mediafire, and watch them where and when you want.

You can use either one of them to paste pics and vids into forums and stuff like that.

Just ask if you have a question.