iTerm2 integration (so you don’t have to learn any commands):

tmux -CC [COMMAND]          # do the iTerm magic

Some really basic commands (note I rebound C-b to C-x, see below):

C-x ?                       # get help

tmux ls                     # list sessions
tmux new -s NAME            # create a session
tmux attach -t NAME         # attach to a session
C-x d                       # detach from a session

Window management:

C-x %                       # vertical split
C-x "                       # horizontal split
C-x <arrow>                 # switch to a pane
C-x {                       # swap panes}

Scrolling:

C-x [                       # scroll mode (use arrow keys)
q                           # exit scroll mode

Slightly more advanced stuff:

# rename a session
tmux rename-session -t OLDNAME NEWNAME

# configure prefix in ~/.tmux.conf
unbind-key C-b
set-option -g prefix C-x