All the hadrons are built up of different combinations of quarks and antiquarks. The quarks are kept together by the strong interaction that is mediated by gluons. Even though the quarks have fractional electrical charge, all hadrons always have integer electrical charge.

As mentioned earlier, the baryons are built up of three quarks. Neutrons and protons belong to this group of heavy particles. They in turn build up the atomic nuclei in the matter that our universe consists of. These quarks come from the first family.

The proton consists of two up-quarks and one down-quark (uud). The neutron consists of one up-quark and two down-quarks (udd).

Many other combinations are of course possible (e.g. uuu and ddd which give the particles ++ and -) respectively. Combinations of three quarks also from family two and three gives other baryons, but they are all very short lived just as the particles (these heavier particles are collectively called hyperons).

The mesons, the medium heavy particles, consist of one quark and one antiquark. Two examples: the positive pimeson (u, anti-d) and the negative K--meson (s, anti-u). Note that one and the same composition of quarks exist in different excited states which give rise to new very short lived particle with higher masses.

There is an interactive part of the animation "The Fireworks of Particles" ("Play with elementary particles!") where you can construct hadrons out of different quarks.