Sessions run in the background and can be detached and reattached. A session contains windows and persists even when you disconnect. This is useful for remote work—if your SSH connection drops, your session is still running.

$ tmux                                      # create a new unnamed session
$ tmux new-session -s work                  # create named session
$ tmux list-sessions                        # list all sessions
$ tmux attach -t work                       # attach to session "work"
$ tmux attach                               # attach to most recent session
$ tmux kill-session -t work                 # kill session "work"

Within a session, use these key bindings (prefix is Ctrl+B by default):

Ctrl+B d            detach from current session
Ctrl+B (            switch to previous session
Ctrl+B )            switch to next session
Ctrl+B s            choose session interactively
Ctrl+B $            rename current session
Ctrl+B :kill-session   kill current session

Each session is independent—windows and panes in one session don't affect others. Sessions survive terminal window closure and SSH disconnection, making them perfect for long-running work.