I've just realised that the idiom 'checking boxes' might be foreign to you. In this case, the 'boxes' are squares on a piece of paper, and 'checking' them refe

I've just realised that the idiom 'checking boxes' might be foreign to you. In this case, the 'boxes' are squares on a piece of paper, and 'checking' them refers to filling them with a tick-mark. I managed to avoid using the term in my comment as I'm from the UK and it's definitely a US thing.