Positively charged ions are called cations. Ions with positive charges have donated the electrons in their outermost shells to electronegative atoms that tend to attract electrons.
Cations have a positive charge because they are electron donors. These atoms have few electrons in their outermost shell and don't hold on to them well. Atoms have a tendency to fill their outermost shells with the goal of having the full complement of eight electrons in these shells: This is the most stable electron arrangement. To get this stable arrangement, certain atoms give away electrons and some collect them. When an atom loses electrons, the number of protons in the nucleus no longer balances the number of electrons. The net charge on the atom is now positive, and the atom becomes a cation.