We can see their difference if we will write the chemical formula for each compounds/atoms/molecules.
Sulfate is a polyatomic ion; a negatively charged ion (anion) which contains more than one atom in its structure. It has the the formula `SO4^(-2)`
Sulfur is an element. It has no charge and is therefore neutral molecule. It is written as S
Sulfide is a monoatomic ion; a negatively charged ion (anion) which is singly in nature. It has a formula of `S^(-2)`