With the keyboard, you can switch windows by typing C-x o
other-window). That is an o, for “other”, not a zero.
When there are more than two windows, this command moves through all the
windows in a cyclic order, generally top to bottom and left to right.
After the rightmost and bottommost window, it goes back to the one at
the upper left corner. A numeric argument means to move several steps
in the cyclic order of windows. A negative argument moves around the
cycle in the opposite order. When the minibuffer is active, the
minibuffer window is the last window in the cycle; you can switch from
the minibuffer window to one of the other windows, and later switch
back and finish supplying the minibuffer argument that is requested.
See Minibuffer Edit.
The usual scrolling commands (see Display) apply to the selected
window only, but there is one command to scroll the next window.
scroll-other-window) scrolls the window that
C-x o would select. It takes arguments, positive and negative,
like C-v. (In the minibuffer, C-M-v scrolls the help
window associated with the minibuffer, if any, rather than the next
window in the standard cyclic order; see Minibuffer Edit.)
If you set
mouse-autoselect-window to a non-
moving the mouse over a different window selects that window. This
feature is off by default.