The charge of an ion is the number of electrons it has gained or lost. The cations are the ions that lose electron and thus are rendered positively charged. On the other hand, anions are ions that gain electrons and hence become negatively charged. For example, sodium atom loses an electron and becomes the cation (`Na^+` ), whereas chlorine gains an electron and become negatively charged anion (Cl^-).
Here as can be seen iron has lost 3 electrons and hence is positively charged with a charge of +3. The iron ion with a +3 charge is also known as ferric or Fe(III) ion.
Iron can also have a +2 charge. This ion is also called as Ferrous or Fe (II) ion.
Hope this helps.