To Create A Session

tmux new-session -s turnip
tmux new-session -d -s cityscape    # start detached

To Create A Window

tmux new-window -n <new-window-name> -t <session-name> <cmd>
tmux new-window -n <new-window-name> -t <session-name>:<window-number> <cmd>

Explicit Window Number

To avoid the

create window failed: index 2 in use

error use an explicit window number:

tmux new-window -n <new-window-name> -t <session-name>:<n> <cmd>

Example

This is a random script from my pi3 which starts up some services written in Python.

• One receives UDP packets and sends wakeonlan packets (I haven't succeeded sending them from Windows machines via command line tools, so resorted to sending UDP to my pi3).
• One provides a HTTP interface for sending Wakeonlan packets. This enables me to wake devices from my mobile via a web browser. It also, for Linux targets, allows to sleep and shutdown via ssh.
• The other is a process which manages multiple mpd (Music Player Daemon) instances around my LAN. This script is a @reboot entry in my pi3's crontab.

#!/bin/bash
start_wol_all() {
  (
  cd ~/wol
  tmux new-session -d -s wol
  sleep 1
  tmux new-window -n mpdmgr_http -t wol:1 p mpdmgr_http.py
  sleep 1
  tmux new-window -n wolsrv_http -t wol:2 p wolsrv_http.py
  sleep 1
  tmux new-window -n wolsrv -t wol:3 p wolsrv.py
  )
}
start_wol_all