Protons are very stable particles that scientists classify as hadrons. They live in the atomic nucleus alongside neutral particles called neutrons. If you zoom in closely, you will see that a proton is made of three smaller pieces.
These tiny subatomic pieces are called quarks. A proton always contains two up quarks and one down quark. A fundamental interaction called the strong force locks these three quarks tightly together.
Tiny particles called gluons carry this force back and forth between the quarks. Each proton has a positive electrical charge of +1. This perfectly matches the -1 charge of a single electron.
The heavy, positive protons pull constantly on the light, negative electrons. This strong electrical pull holds the entire atom together. It also dictates exactly where the outer electrons will travel.
This electron arrangement ultimately decides how the atom will react with other chemicals. Normally, identical positive charges strongly push each other away. This means packed protons naturally want to fly apart.
However, a special strong nuclear force steps in to prevent this explosion. It acts over very short distances to overpower the outward pushing force. It glues the protons and neutrons together into a tight, stable core.
Free protons are incredibly stable on their own. They do not naturally break down over time. In fact, a solitary proton can last longer than the universe has existed.