Richard Feynman once said (as related in his book Six Easy Pieces: Essentials of Physics Explained By Its Most Brilliant Teacher):
If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) thatall things are made of atoms--little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied...
Feynman was right to indicate that this is a powerful statement, but he also knew that it wasn't the end of the story, either. The atom is not, as the ancient Greeks believed, the smallest, indivisible constituent of matter. Feynman himself helped in fact to crack open the atom as part of the Manhattan Project, and then later was in a tight race with Murray Gell-Mann to figure out what made up the protons and neutrons in the atomic nucleus ... an effort that ultimately ended in quantum chromodynamics.
Today, it can be a bit dizzying trying to sort out all of the various particles that physics have found when they began banging tiny chunks of matter together in particle accelerators. But if you want a good starting point, may I humbly recommend our very own Particle Physics Fundamentals, which lays out the major categories of particles and how they relate to each other.