Using a checkbox in pyqt

1) I have a checkbox called "ch_check" in my UI created with Qt designer

2) I have a simple function that should go:

if ch_check.isChecked():
    dothis
else:
    dothat

How would I do that? Do I need to connect the checkbox somehow first? All the examples I found so far use checkboxes to fire off functions and whatnot while completely ignoring this basic usage. I found this question but it's not answering how to address the existing checkbox: How to check if a checkbox is checked in pyqt