Ctrl+b " - split pane horizontally.
Ctrl+b % - split pane vertically.
Ctrl+b arrow key - switch pane.
Hold Ctrl+b , don't release it and hold one of the arrow keys - resize pane.
Ctrl+b c - (c)reate a new window.
Ctrl+b n - move to the (n)ext window.
Ctrl+b arrow left/right/up/down - go to another window
Ctrl+b [ to activave scroll. After that Arrow UP and Down, to exit this mode, q