Linking GUI to Program

I have developed a project which requires GUI to allow the user to select a specific folder which contains the test data which will be subjected to subsequent processes. I am unable to send the pathname which I have defined using a button to the program wherein the test dataset is processed.

Can anyone please suggest me how to send the selected pathname from the UI to the program?

Thanks!

[Jan]

It is hard to guess, what you exactly want: What is "sending a pathname"? You call function with input arguments. But which "program" do you want to "send" what?