The Callback Functions

hi i am really new to matlab gui. i have been trying to learn some basics
from the internet but i am still unable to understand matlab gui very well. I
do not know how to pass "Values" from one function to another.

i have a burning question:

i have made a popupmenu which has a list of videos and a push button.

I would only like to Select the videos without them playing, but only able to
play them after i have press my push button, heres my code under the
popupmenu's callback :

switch get(handles.popupmenu1,'Value')
case 1
winopen('Ma3.wmv');
case 2
winopen('Ma5.wmv');
case 3
winopen('Ma6.wmv');
case 4
winopen('Ma4.wmv');
end

Problem: i do not know how to prevent the video from playing when i select
them from the popupmenu and how can i make use of the push button as the
"Activation" ?

Please help me, i am really out of wits... Thank you...