What’s the best thing to do when one comes into a large sum of money?

The best use case for money is to earn more money.

The next best is to swap it for whatever you want.

If you are at a point in your life where you have all the money you want for the current moment and the forseeable future, spend the money however you want that makes you happy.

If you are not at that point, consider what investments and debt repayments you can use.

If you don’t know, consider ETFs or government bonds.