|Electrons are fundamental particles and, as far as we know, cannot be made simpler. The electron is a member of the lepton family of fundamental particles. |
Protons and neutrons are not fundamental and can be broken down into smaller, fundamental parts. Each proton and neutron contains 3 particles called quarks.
Quarks and leptons are fundamental particles. We think that all of matter is made up from these two families of particles.
The model that describes quarks, leptons and the forces between them is called the Standard Model. You can find out more about this in the resource A world of particles.