Welcome to the Ranch
I think you are going about the whole exercise the wrong way, I am afraid. You appear to be starting from a GUI and trying to get that to calculate, which I think is the wrong way to go about it.
How would you create a calculator without a GUI? Get that working, so you can call
add(123, 456) or
divide(123.45, 678.9) and get it to return an answer. Only then should you think of putting a GUI atop it.
Why on earth are you using Frame, or the show() method? It would appear you are learning programming practices which are 15 years out of date. Look up
Component#show() and see what it says about it.