Alder's razor is a way of thinking that says, "the simplest explanation is usually the best." This means that if you have a problem, the easiest answer is likely the right one.
Think of it like this: Let's say you come home and your toy is broken. You might think that someone came into your room and purposely broke it. But when you ask around, you find out that your little brother accidentally knocked it off the shelf. The simple answer is usually the right one.
Alder's razor is important because it helps us not overcomplicate things. Instead of thinking of all the possible answers to a problem, we can go with the simplest one and save ourselves a lot of time and effort.