This example (https://www.scirra.com/tutorials/257/lets-make-a-calculator ; the first one that poped on google) shows many things not related, but it does eventually explain how to do so.
"Add an event-> On start of layout -> Action -> TextBox -> Set Text -> textbox.
If you run your project, you'll see the textbox with a 0 there. It's working. :)"
But for me this is not working. If I enter only the name of a global variable, nothing shows up in the text box. Even in the the calculator example, if I run it as it is, nothing shows up in the text area.
I've found a way around, it's to enter ""&variable in the text feild. But is it suppose to be like that ?