How to get the most out of Reminders, the best application made by Apple that's also totally free - Business Insider:

The best application Apple makes is Reminders. Released in 2011 as part of iOS 5, Reminders lets you create to-dos that sync across all your Apple devices, including iPhones, iPads, and Mac computers. You don't need a good memory if you know how to use Reminders, which can be prioritized and shared in different ways. It's like having a superpower. ....
https://www.businessinsider.com/apple-reminders-app-tips-tricks-how-to-use-2019-2