Windows are tabs within a session. Each window is independent but shares the session state. You can have multiple windows open, switch between them, and each window can contain panes.

Create and manage windows with these commands:

$ tmux new-window                   # create window in current session
$ tmux new-window -n build          # create window named "build"
$ tmux list-windows                 # list windows in current session

Within a session, use these key bindings (prefix = Ctrl+B):

prefix c            create new window
prefix n            next window
prefix p            previous window
prefix l            last window (toggle)
prefix w            choose window interactively
prefix ,            rename current window
prefix &            kill current window
prefix 0-9          select window by number
prefix '            choose window by name

Windows are numbered starting at 0. When you create a new window, it gets the next available number. You can reference windows in commands like tmux send-keys -t session:window "command". Each window has its own layout of panes, and switching windows also switches the active pane.

Closing the last pane in a window kills the window. If all windows in a session are killed, the session exits.