Okay, so let's imagine you are building a really big tower out of blocks. You have different types of blocks - some are red, some are blue, and some are green.
Now, imagine that instead of building a tower, you are trying to solve math problems about the blocks. You want to figure out how they relate to each other and what rules they follow.
Lie algebra cohomology is like doing math problems with blocks, but instead of red, blue, and green blocks, you have different types of "math blocks" called Lie algebras.
Just like how you can build a tower with blocks, you can build more complex mathematical structures using Lie algebras. But you need to understand the rules that these Lie algebras follow in order to build correctly.
Cohomology is a way of checking these rules to make sure everything is working as it should be. It's like double-checking your math answers to make sure you got it right.
So, in summary, Lie algebra cohomology involves doing math problems with different types of "math blocks" called Lie algebras, and using cohomology to double-check that everything is following the correct rules.