Until these commands are in my muscle memory, I keep them here. C-b
means, of course, the prefix key.
C-b %
split pane vertically (into a left and right pane)C-b "
split pane horizontaly (into an upper and a lower pane)C-b <arrowkey>
switch to another paneC-b C-<arrowkey>
enlarge the current paneC-b q
show pane numbers (press key to jump to pane)