Please explain checks to me

I’ve been reading the book in anticipation of playing a game with my kids, who are so excited that it seems I have promised we will play tomorrow. But I am very confused about checks. Will someone please explain how they are earned? An in-game example would be great; I can’t seem to picture it.

I think I understand how checks are spent, but if someone would explain that to me in words of one syllable as well, I’d feel more sure of myself.

Of course, as soon as I wrote this the penny dropped and the pieces came together. I think I’ve got it now.