Formal Charge (FC): associated with any atom that does not exhibit the appropriate number of valence electrons. This means that the valence electrons (VE) are not what they normally are. +VE means that electrons were donated and -VE means that electrons were attained from another atom. FC of atoms are a useful for electron book keeping and helpful in determining reactivity of a compound. If you struggle to determine formal charge you can draw the lewis dot structure which can help you visualize it better. With enough practice one can determine Formal charge at a glance.
In neutral compounds, there can be individual atoms with charges. The molecule remains neural when the overall charge is 0. This means that the charges canceled each other out.
Charges are useful for insight on or predicting reactivity.
Unless you have a metal involved, the FC will either be neutral or +1/-1
There are two equations you can use to determine FC. This equations include:
FC = (Group Number) - (#electrons in Covalent bonds) - (#LP)
Group Number is the number of VE in the neutral atom
FC = (Group Number) - (#VE around atom in molecule)
This is the equation used above