Particle physics is the study of nature at it's most fundamental, a continuing attempt to find the basic building blocks of...well... everything, those fundamental particles that are not built from anything smaller. Although nowadays it is not just the search for ever smaller particles, but also the study of their properties, forces and interactions.

The atom was at one time thought to be this basic building block until they discovered that the atom itself had a structure of it's own and was comprised of a, positively charged, tiny nucleus surrounded by a cloud of, negatively charged, even tinier electrons. The nucleus was then discovered to be made up from, positively charged, protons and,neutrally charged, neutrons (ie, no charge). Then along came even smaller particles called quarks that are the building blocks of protons and neutrons.

Electrons, along with muons, tauons, and neutrinos are known as leptons.

While an atom is tiny, the nucleus is ten thousand times smaller than the atom and the quarks and leptons are considerably smaller still. We don't know exactly how small quarks and electrons are but have been estimated to be at least one hundred millionth the size of an atom.

We now have two basic matter particles, quarks and leptons. Quarks behave differently than leptons, and for each kind of matter particle, there is a corresponding antimatter particle.

There is a third basic building block, gauge bosons which act as carriers of the fundamental forces of nature - photons, probably the best known example of gauge bosons, are the carriers of electromagnetic radiation of all wavelengths (including visible light, gamma rays, x rays, radio waves, etc.), three other examples are W and Z bosons, gluons, and gravitons, although gravitons (hypothesized mediators of gravitation) have never been observed.

Therefore, the fundamental building blocks of nature (read, the whole universe) are quarks, leptons, and gauge bosons (not forgetting their antimatter equivalents.) However, remember that the atom was once considered the fundamental particle until it was discovered to have structure, it is still quite possible that our latest fundamental particles will also be found to have their own structures.

The main goal is to understand as much of the physical universe, and life, as possible, by understanding the basis that everything is built from. No matter how large or small, simple or complex these structures may be, everything from virus to dark matter to black holes are all built from fundamental particles, the trick is identifying and understanding them.