Couple more things

In a post I have the “Share This:” section set up for things like Twitter. When you click the Twitter one it just gives the post title and a link. How can I change this so that it also gives the Twitter account name every time without manually doing it each time?

For my front page and my main video page I want the video and not an image to pop up, so I am wondering how this is done. I know to have an image there you put it in the “Feature Image” location of the post. So would I put the video there? 

How can I customize the “About AUthor” section that shows up with each post?