CTRL+a c: New terminal
CTRL+a SPACE: next terminal
CTRL+a BACKSPACE: previous terminal
CTRL+a [x]: Switch to x'th terminal
CTRL+a ": Switch between terminals using the list.
CTRL+a |: Split vertically
CTRL+a S: Split horizontally
CTRL+a Q: Unsplit
CTRL+a TAB: Switch between splits
Screen can be (misused) to share a terminal between multiple users on a host. For that to work one user has to initate a screen session and share (e.g. the session name) with the other users.
The following example creates a session with the name shared and another user then connects to it.
# create session and login user1> screen -L -S shared # create to session with different user user2> screen -x shared