IDEF0 is a way of drawing pictures to explain how things work. Imagine you have a bunch of Legos and you want to build a house. You start by making a plan on paper that shows how each Lego piece should fit together to make the house.
Well, IDEF0 is kind of like that plan, but instead of Legos, it shows how different parts of a big system fit together to work. For example, let's say you want to understand how a car is built. You draw a box for the car and then draw lines that show all the parts that make up the car, like the wheels, the engine, and the seats.
But that's not all! You also draw arrows that show how all the different parts of the car work together to make the car go. For example, the engine makes the wheels turn, which makes the car move forward.
IDEF0 is really helpful because it helps people understand how complicated things work, even if they don't know much about them. It also helps people figure out where things might go wrong in a system and how to fix them. So, just like how you need a plan to build a Lego house, you need IDEF0 to understand how big systems work!