Each proton and each neutron contains three quarks. A quark is a fast-moving point of energy. There are several varieties of quarks. The sum of the charges of quarks that make up a nuclear particle determines its electrical charge. Protons contain two up quarks and one down quark.
Neutrons contain one up quark and two down quarks.
The strong force counteracts the tendency of the positively charged protons to repel one another. It also holds together the quarks that make up the protons and neutrons.