what to do with the double when you shell a program

So i shell a program to open it and it returns a double. What can i do with this double? i would like ot use it to make sure the focus is on the program i shelled. If you know where i cna find info on this it would be appreciated.

[Frans C]

You can use it with the AppActivate function to make sure it has the focus.

can you elaborate on that? and how do i close the program i had shelled?