Proton

A proton is a positively charged subatomic particle found in the nucleus of an atom.

What it does
First of all, the number of protons in the nucleus decides what the element is. For example, if there are 3 protons, then it is lithium (Li), if there are NOT 3 protons, then it is NOT lithium. This is the atomic number, it is NOT to be confused with atomic mass, which is mass of protons AND neutrons in the nucleus combined.

If the protons are positive, then why doesn't the nucleus explode from the rule "like charges repel"?
Good fucking question! Your answer: The neutrons are neutral in charge! Their job is to keep the protons together like velcro keeps 2 likecharge magnets together, it only works at a very small proximity, it is called "strong nuclear force"!

How it was discovered
Geiger-Marsden Experiment was an experiment thought up by Ernest Rutherford, and carried out by Hans Geiger and Marsden! It involved trying to test the plum pudding model (which taught that electrons were dotted around in a pudding of positive charge) by blowing up one of the "pudding" atoms of a gold leaf with alpha particles.

What ACTUALLY happened was different from what was expected, the rays of alpha particles were being reflected and some of them went through the gold leaf!

This proved that the positive alpha particles were being repelled by a positive core, but were being let through partially because much of the atom was unoccupied by matter.