In the Codecademy lessons, they don’t actually use promises like they would be used in the real world. However, they just want you to get a good understanding of its syntax, and how it works (they also mention a few times how it would work in the real world)
Promises are used when fetching data from somewhere else - this could be your database, an API, etc.
Let’s just say you are fetching data from your database - you want to know how many users signed up to your program. To do that, you would simply take the number of users in your database, but this could take a bit of time (a few seconds). So, you would use all the methods that Codecademy tought you in the lessons (either .then() / .catch() or async/await), to handle the retrieval of data from your database