You have probably seen how an atom consist of a nucleus, with around that nucleus, electrons in fixed orbits around the nucleus, similar to planets orbiting the Sun. Even though this description works fine for creating a sense of intuition, it is not quite complete. Some scientists in the early 20th century figured out that objects that are really really small (like electrons), start acting really really weird. One way in which they act weird, is by not having a well-defined position. That means: you can’t say an electron is exactly at position x at time t (like you could do for a marble, for example), you can only say with a certain probability that you could find an electron at a certain point in space and time. In other words, if you would make yourself really really tiny, and go sit on the nucleus of a hydrogen atom while looking at the electron, you wouldn’t simply see an electron following a planet-like orbit. While the electron moves around the proton, you would sometimes see it very far away from the proton (though the probability for this, is very small) and, most of the times, very close (there’s even a rather large probability that the electron will pop up inside the nucleus!). As time progresses, you will see the electron jumping closer and further away, while it rotates around the nucleus.