Exactly how do I utilize the various event methods that widgets have? Say I have a comboBox(drop down list) and I want to initiate a function every time someone changes the choice. There is the changeEvent() method in the documentation but It would be great if someone explains to me with a piece of code.
This is a pretty broad question.  I recommend checking out the many tutorials on Youtube.com.  
However, in your init method, put something like this:
self.ui.charge_codes_combo.currentIndexChanged.connect(self.setup_payments)

In my example, the combo box was placed on a form in Qt Designer.  Self.setup_payment is a method triggered by the change in the combo box.
I hope this helps!
How to use pyqt widget event() method?