As the man page states, Screen is a full-screen window manager that multiplexes a physical terminal between several processes (typically interactive shells). A process (shell or command like ls) can be attached to the screen command/session. The screen session won't die or exit until terminated by the attached command/shell. This is useful when working over a flaky network connection. Screen can multiplex commands into a single window so it makes it convenient to open new shell sessions in the same window.
Starting a screen session
You can start a new screen session just by typing 'screen' command. You can name your screen session using -S option as follows:
screen -S screen-getting-started
Adding configuration options to screenrc file
Logging screen window to a screenlog file
Screen can log it's window output to a screenlog file. This can be done by invoking screen with -L option.
Viewing screenlog file
Screen log file contains escape characters and hence it's not directly human readable. You can get pretty output using less command with -R or -r options. See stackoverflow answers for hints.