Okay kiddo, imagine you have a set of blocks with different colors. You can use these blocks to build structures like towers or houses.
Now, let's say a friend gives you a rulebook with instructions on how to build different structures using these blocks. The rulebook tells you which colors to use and how many of each color you need.
This rulebook is like a countably generated module. A module is a mathematical concept that's like a set of blocks you can use to build things. A countably generated module means that there's a specific set of instructions you can follow to build anything you want using the blocks in the module.
In other words, if you have a countably generated module, you know exactly which building blocks you need and how many of each you need to use to build anything in that module. Just like how the rulebook tells you which blocks to use and how many you need to use.
Does that make sense, kiddo?