We need to create a button. Make a simple square, select it and press F8 to make it a library object. Choose button and name it "Rub Button" for example and press ok. Select your button and press F8 again to insert your button in a Movie Clip (MC) now. Name it "Rub MC" for ex, choose Movie Clip and press ok. Double-click on your MC "Rub MC" and fill the occur name like "Rub". The occur of a MC is the name targeted by any action with script, it's totally different than the name of the object in the library, this last one doesn't matter as contrary as the occur name !
Now, go into your "Rub MC" (right-click ---> modify in place), name the layer you have "Button" and make a new one at top called "Label". Choose the text field tool (press "abc" button) and type "?" in (It's just to be sure text is visible; ne same color). Adjust it according to your button size, right click on it -----> Properties.
Name the var of your text field "Label", disable first option (smthg like "keep border & bgd"), enable options like "disable text edition" & "disable text selection" (allowing to don't have text cursor on roll over text field), enable option like "include font", press ok and finally, customize your font, color and size text. Now return back on your main scene.

You should obtain this :

Note : I've set to my file a 150*350 size and 24 f/s (ctrl + m).