Ask people where they go to “get work done”, where they are at their most productive: They almost never say ‘the office’. Or if they do, it’s before or after hours.
Work is like sleep, it proceeds in cycles. You have to go through the light-sleep / light-work cycles to get to the meaty stuff. Every time you get woken up / interrupted, you start from scratch.
Screen is a terminal multiplexer. In simple language, screen allows you to ssh into a machine and open several sessions at once, and leave them running. If you work on remote machines, you need screen.
Install it
sudo apt-get install screen
Configure it
The .screenrc file in your home directory configures screen. Use this to get you started: