An atom's nucleus is constructed of protons and neutrons. Protons have an electrical charge of +1. Neutrons are neutral -- they have a charge of 0.
A quark is a fast-moving point of energy. Three quarks make up protons and neutrons; quark-antiquark pairs make up particles called mesons.
The quarks within protons, neutrons, and mesons are held together by the strong force.
A photon is a particle that carries electromagnetic radiation (including everything from radio waves to light to gamma radiation). Photons have no mass and no electrical charge.
More about the radioactive decay of carbon
Carbon14 is unstable. Its nucleus contains 6 protons and 8 neutrons. When carbon14 decays, one of its neutrons changes into a proton, shooting off an electron in the process. The atom, which then contains 7 protons and 7 neutrons, is no longer carbon -- it is Nitrogen14.