How do I tell my new boss they are not good at explaining things to me?

I started a new job recently, and while I love my bosses and think that they are very good at what they do, they are both extremely scatter-brained (hence hiring me) and NOT very good at explaining how things work to me. I am running into several situations where they seem to be frustrated with me for not “just knowing” how things work, and I’m getting irritated. Suggestions?