The electron has no known internal structure. As far as we know its a fundamental particle and isn't made up of other things, the way protons or neutrons are made up of quarks held together by gluons.

An electron's location is subject to all sorts of rules. The Heisenberg uncertainty principle says that the more we know about a particles momentum (mass*velocity), the less we know about its position, and vice versa. This is not a matter of the observer effect (measurement upsetting one of these values), as some people state, but something fundamental due to the wavefunction nature of matter. The location of a subatomic particle is determined by its wavefunction (Squared) - where the wavefunction is big you have a high probability of finding a particle, and where it is small you have a small probability to find a particle. the wavefunction is a probability density function - the probability of finding a given particle at a given place in a given time.

The next important idea is that subatomic particles can be considered both particles and waves, and thus have a wavelength. High momentum particles (high energy) have a short wavelength, low momentum (low energy) particles have long wavelengths. Waves are disturbances spread out in space, and we can identify the distance between two peaks (the wavelength), but then we wouldn't know anything about its position - it could be in lots of places.

To localize a wave you add together lots of waves (into a localized wavepacket) until the resulting wave gives you areas where you are likely to find a particle where those added waves overlap in crests, and areas where you are unlikely to find the particle where those added waves overlap in troughs. This is a tradeoff, though - you are still subject to the heisenberg uncertainty principle so the more you know about the location, the less you know about the momentum. Thus the electrons, which move very quickly, and are interchangeable with one another being identical to each other, appear to exist as a cloud of probabilistic locations. They aren't themselves a cloud, rather their position is always uncertain until directly measured to a high degree of certainty.

Now you may say "but we know electrons live in orbitals around atoms - how can we know that if we can't know their precise positions". This is because electrons obey the pauli exclusion principle, which states that two or more particles with half integer spin (fermions of which the electron is one, which have antisymmetric wave functions) cannot have the same set of four quantum numbers -

n (the shell number or general region for value of energy of the electron),

l (orbital angular momentum/the shape of the orbital),

m sub l (the magnetic orientation of the orbital), and

m sub s (quantum spin, which for fermions can be +/- 1/2). (the minus is what makes fermions antisymmetric)

This principle is why electrons are more likely to be found in some places around an atom described as shells, and thus why electrons exist in discrete locations around an atom and why atoms and chemistry exist. The reason for the pauli exclusion principle is also wave related - I'll link a video below:

https://www.youtube.com/watch?v=Zlp2GQ3OLeE

This was a pretty surface level explanation - we didn't even get into the dirac equation (which is where the existence of antimatter was first derived) or spinor theory! but I think its good enough to have some understanding of why the fundamental wave nature of subatomic particles leads to uncertainty in their location, which means they appear to live in a cloud around atoms.