Imagine you have a bunch of different colored candies (red, blue, green, etc.). Now imagine your friend has a different bunch of candies with different colors. Even though your candies look different from your friend's, they are still both candies. And if you both have the same amount of candies, you can say that you have an "equivalent" amount of candy.
Now let's imagine that you went to school in a different country where they use a different system for teaching and grading. When you come to a new country and want to continue your education, the new school might not really understand how to compare your grades and classes from the old country to their own system. You might have learned different things or had different standards.
That's where an academic equivalency evaluation comes in. It's like a person who can look at your old school records (sort of like looking at your candies) and figure out how they match up with the new school's system. They can say whether your old grades and classes are "equivalent" to the ones you need to take at the new school.
In summary, an academic equivalency evaluation is like comparing your old school records to the new school's system and saying whether they're the same or similar enough to count as the same thing.