What is it good for?
Let's say you are working on a remote computer but your laptop's battery is low, or your connection is not very good, or your run takes forever and you have to head out with your laptop shut, the screen program is here to ensure your code can still run even when your local computer is shut. It let's things run in the background.
How to use it?
Log in to the remote computer
In the terminal prompt type 'screen'
You can keep working in screen mode, and if your connection dies you'll be able to get back to this screen (literally!)
You can detach screen by typing Ctrl+a (puts you in screen mode) and then Ctrl+d (detaches from screen), this will let your simulation run in the background and you can always get back to it.
How to return to your screen? type screen –r (reattach)
That's it, you are all set.