All these things and more are composed of just three kinds of building blocks. Combinations of these three simple bits comprise everything of any consequence in the physical universe. They are The Electron, The Proton, and The Neutron.
The Electron. It carries a negative electric charge, meaning it repels other electrons and is attracted to positive charges. It is very lightweight. Mysteriously, every electron has exactly the same mass and charge as every other electron. As far as the best instruments are able to detect, the electron has no size, but is a single geometric point.
The Proton. A massive particle with a positive electric charge, exactly equal and opposite to that of an electron. Protons have a diameter of about a trillionth of a millimeter. They repel other protons and attract electrons. They are also slightly sticky. Although they repel each other, if you get them close enough, they will stick together.
The Neutron. This weighs about the same as a proton and is about the same size. It is also sticky, like a proton. But it has no electrical charge and is therefore very hard to control, to hold, to detect, or do much of anything with.
When a bunch of protons are mashed together, they sometimes stick and form a ball called a nucleus. They find it easier to do this when some neutrons are included to add more "stick" and help them overcome their mutual electrical repulsion.
When a nucleus forms, it has a strong positive charge equal to the number of protons. Eventually, an exactly equal number of electrons gets involved because of the strong electrical attraction. Then a funny thing happens: the electrons are unable to get closer than a certain distance to the proton/neutron cluster and they end up hovering around in a kind of layered, structured cloud. That's what we call an atom.
How big is the nucleus? If an atom were the size of a sports stadium, the nucleus would be about the size of a marble laying in the grass at center field. Except there would be no grass. Electrons would be the spectators sitting in the stands, except there would be no stands, just electrons.
Carbon, for example, is the kind of atom you get when any 6 protons form a ball. Some neutrons are needed to help them hang together. Zero to two neutrons isn't enough, and results in an unstable ball that almost instantly disintegrates due to the proton's mutual repulsion. Three to five neutrons is almost enough and results in a nucleus that survives for a few hundred milliseconds to a few minutes. The more neutrons, the more stable it is.
With 6 or 7 neutrons, the 6-proton neucleus (Carbon) is stable. 98.9% of Carbon atoms have 6 neutrons, while 1.1% have 7. We call these "isotopes" "Carbon-12" and "Carbon-13."
Carbon-14 is famous for its ability to indicate the age of things that contain carbon. In the atmosphere, carbon is exposed to radiation which "activates" some small percentage of it. The result is Carbon-14 which is unstable but which decays very slowly. About half disappears every 5730 years. That rate of decay can be used as a kind of clock to determine how long a carbon sample has been "out of action" as it were.
Electrons, Protons and Neutrons are all that are needed to create every element on the periodic table, and therefore every chemical compound, and therefore every object or substance you will ever encounter in this physical universe. It is true that protons and neutrons are themselves composed of smaller pieces, but they play no significant role in everyday life.
Only three things to keep track of? Anyone can cope with that. And you thought Science was going to be hard.
