if __name__ == '__main__':

When Python is interpreting your code, it has an internal variable called __name__ which will reveal the "namespace" that your code is being run from. This is so you can have it do one thing if called directly, or do another if imported by some other code with an import statement.

You can use this to identify if your code is being called directly, for example if you launch it from the CLI command line as with the python mycode.py command. In this case the variable __name__ will return the string '__main__'.

The reason you want this is so that you can perhaps call a function to start your code running. For example, if your code is designed to be run directly (as a game perhaps) this could call a function or class method to start your game.

But let's say your code is designed to be used by other code. Perhaps your game is designed so that it can be used as an API library allowing you to reference the leaderboard statistics of your game play. So then your website backend code might import one or more functions from your game and use that to show that leaderboard code. In this case your code won't start your game up when it is imported because __name__ will not equal '__main__' but will equal the namespace that you are importing into.

Long winded, but I am as new to this as you so I am not good enough to explain it better than that. Perhaps some uber python peoples can give you a better answer. :)