I would like create a popoup wich ask to the user to choice a letter for the end of the program but I don't how to do a popup.. Can you tell me please!! thanks sole
If you want a simple way to do this, you can use the express VI 'Prompt User for Input' from the Time & Dialog pallete, although Jack's suggestion (writing your own VI) is better if you do serious programming.
In that case, go with Jack's idea - create a VI which will run until getting the input from the user (let's say using an event structure). Then, set it to "show FP when opened", "close afterwards..." and (very important) to Modal (this will make it stay on top). You can find these in File>>VI Properties>>Window Appearance>>Customize.