Monomorphism is like having one special toy that nobody else can copy. Just like when you have a toy that is unique and nobody else has one exactly like it, a monomorphism is a special kind of function that works in the same way. When we talk about functions, we mean something that takes in some information, does something with it, and then gives us some new information back.
Monomorphism is a function that has a special power - it works in one direction only. It means that if you have two things that look the same, like two toys that look the same to you, but one of them is the real special toy (the monomorphism), there is a special way to tell them apart. This is important because it means that you can't just copy the special toy, you need the real thing.
In the same way, monomorphisms in math are special because they can't be copied. If you have one type of object, like a number or a shape, and you have a function that can take two different objects and turn them into the same thing, it is not a monomorphism, because you can't tell the objects apart anymore. But if you have a function that takes two different objects and turns them into something different that you can still tell apart, then it is a monomorphism.
Monomorphisms are like fingerprints for numbers, shapes, or any other kind of object. It is a way to tell exactly what something is, even if it looks like something else. So, just like your special toy, monomorphisms are one-of-a-kind and really important.