The proton carries a charge of +1 (in units of the electron charge) and the neutron is neutral (zero charge). Protons and neutrons are themselves made up of quarks as this schematic picture indicates. In the quark model, the only difference between a proton and a neutron is that an up quark has been replaced with a down quark.
The little spring is meant to indicate that the quarks inside a nucleon are held together by a force we call gluon exchange.
A nucleon is about 1.6 fm (femto, 10^{-15}, meters) which you might write as 0.0000000000000016 m. That is pretty small, but not much smaller than a nucleus. That is because the force that holds the nucleus together is very short range, so the protons and neutrons in a nucleus are packed together so they are almost touching each other.