In the following image:
The oxygen's top pair of electrons forms a double bond.
But in a covalent bonds, aren't the electrons shared? So won't the oxygen still have these $2$ electrons (that it turned into a double bond) in its outer shell? Leaving its charge as $0$?
So why would its charge change?
I think what is confusing me is what the negative and positive signs mean and how this relates to it's formal charge and its octet.
I know the left structure's oxygen has a formal charge of $0$, and the right hand structure's oxygen has a formal charge of $+1$.
So are plus and minus signs showing formal charge, and not the number of valence electrons?
If so, does the plus sign have nothing to do with the number of valence electrons?