Sub atomic particles are things smaller than an atom.
 Types of sub atomic particles
Some sub atomic particles are components of atoms, like protons, neutrons, quarks, tiny neutrinoes and electrons these are a subset of fermions. There are also bosons of assorted kinds including photons, gluons and possibly gravitons. One notable boson is the Higgs boson which was confirmed to exist in July 2012.
The list of sub-atomic particles is, according to some theories, literally endless, and certainly very long.
Some, perhaps most, sub-atomic particles have anti-matter equivalents, but photons, according to current theories, are the same in matter and anti-matter.
 Quantum effects
Reality on the scale of subatomic level is different from the way reality appears on the macroscopic scale that we normally observe. We evolved to understand reality on the our natural scale; reality on the subatomic particle scale is perplexing and counter-intuitive to us.