You can see the effect of installing multiply-by-seven by
evaluating the following sample. Place the cursor after the following
expression and type C-x C-e. The number 21 will appear in the
echo area.
(multiply-by-seven 3)
If you wish, you can read the documentation for the function by typing
C-h f (describe-function) and then the name of the
function, multiply-by-seven. When you do this, a
*Help* window will appear on your screen that says:
multiply-by-seven is a Lisp function. (multiply-by-seven NUMBER) Multiply NUMBER by seven.
(To return to a single window on your screen, type C-x 1.)