Screen is great for long running tasks, where you want to log in every few hours and days and keep your session alive indefinitely.
To create a new screen, do
screen -Rd screenname
This will also reattach an existing screen with that name.
Once you're in the screen, CTRL+A
will bring up the menu, d
detaches the screen. You can close your shell, screen and all applications running inside of it will remain alive.
CTRL+A
Esc
Page up/Page down
Esc
takes you back again