appending text from button into text box

I'm looking for code that will paste a bit of info into a text box on an MSAccess form. I have a form that has buttons on it. Each button has a word associated with it (say, "box", "circle", "tree", etc.) . I want the user to be able to click the button and have the word "box" appear in the text box. If they select another button (ie. "tree"), I want that word to be appended to the first word (ie. "box, tree"), and so on. Can someone offer me a script I can put into an Access Expression or Macro?

tia
Tom