If you want to replace the default "About you" output for the article author box and the article poster's username in various parts of the article forum view and article post then use the following Field ID's under Users > Custom user fields:
The rest of the other fields are optional. You'll want "Single-line text box" for author name and "Multi-line text box" or "Rich text box" for author about. The author about allows use of BBCode.
Suggested "Author name" description: If specified, this will replace the username displayed on article pages.
Suggested "Author about" description: If specified, this will replace the about you description displayed in the author box on article pages.