How to use 'SCREEN' command in linux?

To start a screen session:

$screen -S screenname

We have now started a screen session with name `screenname`. Lets start a process here for us to understand the working of screen. 'top' command initiates a process that shows the list of processes running on the machine.

$top

Now you find top process running on the terminal.

To suspend screen session do the following.
Press Ctrl + a , z (Press Ctrl + a and then press z)
This would only suspend and does not end the session, so that you can comeback later and check.

Now you are out of screen and at the terminal where you started.

To see the list of screen sessions,
$screen -ls

you should be finding the screenname listed.

To go back to the screen
$screen -dR screenname

you should now find the top command still being executed.

To end the screen
$exit

You can recheck it with `screen -ls` command.

Done !! Now that you have got your hands dirty, you can visit the following resources to know more about it.
http://linux.die.net/man/1/screen