Okay kiddo, so you know how sometimes when we talk about something, we use two words instead of one? Like "peanut butter" or "salt and pepper"?
That's called a "dvandva". It's a fancy grown-up way of saying two words that go together to describe one thing.
People use dvandva a lot in languages like Sanskrit or Hindi, but we use them in English too! It's just not always obvious because we're so used to hearing them.
So basically, dvandva is just when two words make one idea or thing. Cool, right?