A neutron consists of two down quarks and one up quark as well as a probabilistic aspect of strange and anti-strange quarks (much lower level) bonded with gluons. A proton is similar in structure, but includes two up quarks and one down quark with the gluons. In both cases, the main force holding them together in, say, an oxygen nucleus is the strong force, although the electric force between protons is also significant. There is a shell structure for the protons and neutrons that is based on the strong force.<quoted text>
You may explain until the detailed structure of the neutron of an atom.
After that, there are electrons in orbitals surrounding the nucleus, but on a scale much larger than the nucleus (nano-meters rather than fempto-meters). The Pauli exclusion principle produces multiple layers in much the same way as happens in the nucleus, but based on the electric force. The outermost shell is not full, which allows hybridization with other atoms, producing binding and anti-bonding orbitals and thereby molecules of, say, water.