In quantum mechanics, there's uncertainty built into every physical process. Let's say an electron could go left or right at a junction. Before you check, you can't know where the electron is: you say the result is a superposition of electron-going-left and electron-going right.

When you measure the electron's position, you'll find it either went left or right, and depending on how you set up the experiment, it might be that half the time you do it, you'll find left-electron, half the time right-electron. How does each electron "decide" which way to go?

That question is what different interpretations of quantum mechanics try to answer. How do we go from probabilities to single answers? You start with a "wavefunction" that contains all possibilities and end with a data point: you could say the wavefunction collapsed to one result

In the Many Worlds interpretation of quantum mechanics, the wavefunction never collapses. All possibilities happen, they just happen in different universes. If you measure "electron went left" you're not measuring the electron, you're ACTUALLY measuring which universe YOU'RE in.

So next time you are waiting for the result of some process or experiment, if the Many Worlds interpretation is correct, perhaps you're not, in fact, learning about something happening in the world, really. Perhaps what you're learning is what world you actually live in.

(If you want to read more and better things about Many Worlds, check out @seanmcarroll's book, Something Deeply Hidden: https://www.preposterousuniverse.com/somethingdeeplyhidden/ or @FreelanceAstro's about the development of interpretations of quantum mechanics, What is Real?: https://www.hachettebookgroup.com/titles/adam-becker/what-is-real/9780465096060/)