A balance on an exchange, in an app or in a fund is not the same thing as bitcoin in your own wallet. It is a promise from a company to give you bitcoin, or its value, when you ask. Bitcoin was built so that people could hold value without trusting a third party; this tool shows how much of yours still depends on one.
Type rough amounts in each place you hold bitcoin. The tool shows the share you control with your own keys and, for each place, what has to keep working for you to get your coins. It is not a judgment: many people keep some coins with a company on purpose. The point is to know which is which.
Related lessons: Exchanges versus self-custody, ETFs, IOUs and real bitcoin, Custody options, from easy to sovereign, How to read a proof of reserves.