Screen GNU

Start screen
Type screen in the terminal
Detach from a screen session (session remains open)

Ctrl+a d

Reattach to an open screen session

screen -D -R

Quit screen completely (session closed)

Ctrl+a Ctrl+\ 

Controlling windows

Create a new window with a shell and switch to it:

Ctrl+a c

List currently open windows for selection:

Ctrl+a "

Close current window:

 Ctrl+a k 

Controlling Regions

Using regions allows you to display more than one shell on your terminal.

Split the current region into 2 new ones (note: new region will be blank, you need to switch to it then select a window to display in it):

 Ctrl+a S

Switch focus to the next region:

 Ctrl+a TAB

Remove the current region:

 Ctrl+a X 

That should be enough to get started