How to customize the "posted_on" function.

Please help!
I would like to customize the section above the post that says:
“Posted on August 8, 2012 by admin”

Basically what I wanna do is add the author’s Avatar, a twitter icon with link and an email icon with the link…
Now to do that, I assume I have to add an input named “Twitter” under the author’s profile where we can type the authors twitter url.

This is a visual of what I am trying to achieve
https://www.antoniodigitalmedia.com/wp-content/uploads/2012/08/blog.png

Come on.. I know is not that hard
I did try hard to figure it out but it just didn’t happen…

Much appreciated!!!