As much as I like its functionality, the tmux program ux is terribly unintuitive. From the crash course:
tmux new -s session_name
creates a new tmux session named session_name
tmux attach -t session_name
attaches to an existing tmux session named session_name
tmux switch -t session_name
switches to an existing session named session_name
tmux list-sessions
lists existing tmux sessions
tmux detach (prefix + d)
detach the currently attached session
The -s/-t feel like they should not be required. They shouldn't even be different in the first place. list-sessions should just be list, since the -sessions is implicit in all other commands as well. Exiting from a session (ctrl+b d) is another new thing too. If that were at least like vim (which is terrible as well, but esc :q), it would be much easier to interact with. Only after reading the man pages these make sense.