We will start with a Sodium Atom:
This is a Na atom. It has 11 electrons on the shells and 11 protons in the nucleus (blue circle)
Metals as Na can lose electrons from the last shell and it becomes an Ion with a positive charge.
Red dots are electrons. The second picture is from Ion Na and it is called cation because it has a positive charge.
If we draw a neon atom, you will see that it has the same configuration of Na ion, but Neon is a noble gas and it has not a charge:
