To open a new screen
#screen

To detach it
#screen -d

To get list of screens
#screen -list
13827.pts-4.servername

To resume it
#screen -r 13827

To sudo to a different user aaa then use screen
sudo -u aaa -s
script /dev/null
screen

Ref. http://dbadump.blogspot.com/2009/04/start-screen-after-sudo-su-to-another.html