Quantum theory tells us how the very small things in the universe work. Photons, electrons and other particles. It tells us how electromagnetic waves and particles work because they act in very strange ways.
Democritus a Greek Philosopher came up with a theory of matter that suggested all matter is made up of tiny indestructible pieces he named atomos, meaning undivided. Today it is known we can break atoms up it smaller pieces and those can be broken up again.
in the 1800’s E. Goldstein discovered the positively charged particle proton, meaning first. JJ Thomson discovered negatively charged particles we call electrons and in 1932 James Chadwick discovered the neutron a particle without a charge.
Not happy with that explanation scientists then discovered particles named quarks in 1964 done by splitting a proton or a neutron. two down one up quark make a neutron and two up one down make a proton. In elementary particle physics your either quarks, leptons or and bosons or hadrons which cannot be broken down any further.
Bosons family contain photons, gravitons and gluons. photons carry light, gravitons are responsible for gravitational force and gluons hold hadrons together. the most famous lepton is the electron, from which we get electricity. others are muon and tau. Hadrons are either protons and neutrons or omegas etc they are all made up of various combinations of quarks.
Protons and neutrons can be split with a particle accelerator which shoots a beam of particles through a circuit using high energy magnets to get them up to almost the speed of light they are then collided into another particle.
Particles make up matter. there are particles that also make up antimatter, they are thought to negate each other or destroy. the universe was created from excess matter that was not destroyed by its counterpart.
Dark matter also exists, it makes up 90% of the expanding universe. the main one is neutrinos: one billion exist for every single proton and electron.