Source code is like a recipe for a computer. You know how when mom or dad wants to bake cookies, they look at a recipe to figure out how to make them? Well, computers need recipes too.
Source code is a recipe that is written in a special language that the computer can understand. The code tells the computer what to do, step by step, so that it can do whatever it is supposed to do.
For example, if someone wants to make a game, they would write the source code to tell the computer how the characters move and what happens when they touch things.
Once the code is written, the computer can run it and turn it into something that you can see and use, like a game or an app.
So, source code is like a recipe for the computer, telling it what to do so that it can make something for you to use or play with.