What a great questions Giuola. Particle physics is the study of the particles that make up the Universe. There are lots of different particles but we group them together into something called the Standard Model – this is our understanding of all of the particles in the Universe.
We have quarks (that make up protons and neutrons) and particles called leptons (like electrons and neutrinos) as well as particles that carry forces (such as photons in electromagnetism).
Dark matter is NOT in the standard model (yet!), because although we think it is there, we haven’t actually detected a dark matter particle yet – we hope to do this at the Large Hadron Collider in Cern. We think that most of the mass of the universe comes from dark matter and something else called dark energy – everything else that we can see (stars, planets, gas, dust etc) only makes up a small percentage of the mass of the Universe.