Buttons are pretty
simple to do but I'll still show you how to get them
working in your map.
First thing to do is
to read the door
tutorial as we'll be making the button open
these doors, use the example map that is included in
that tutorial.
Okay, somewhere in
your level create a small brush (about 32x32) and
place it where you want the button to be, now select
the button and the right click over the grid and
scroll down to the func>func_button and
you notice that the button you created is now a
func_button.
With that done make
sure that the func_button is selected and now select
one of the doors, when this is done hit CTRL + K and
you should see a blue line going from the button to
the door

Because
we teamed the door together in the door tutorial we
only need to link to one of the doors as they will
open together.
A couple
of other things we need to do
with the func_button is set the angle and wait status, i
need my button to go into the wall slightly so i set the
angle to 90, use the angle thing in the entity dialogue by
pressing N.
If you set
a key to wait and a value at 3 the button will wait 3
seconds before returning to it's original position.