There’s an electron and it is found somewhere around the nucleus, at a certain distance r. Looking at this distance from the nucleus or you as observer and noting down the distance everytime you check the electron, a pattern will emerge/a nice graph will be produced. Sometimes this electron will be inside of the observer, meaning at the same point in space. Initially the position might seem totally random. Your electron has a certain energy since it is moving and is inside a potential (attraction) to the nucleus. 1s means it has the lowest amount of energy possible.