List all active sessions:

screen -ls

Start new session:

screen -S [session-name]

Reattach to existing screen:

screen -r [session-numeric-id]

Detach session (without termination):

Ctrl + a, d

Close existing session:

screen -XS [session-numeric-id] quit

Show help:

Ctrl + a, ?

Create screen, detach and execute command in it:

screen -dmS session-name bash -c '... command ...'