Number of solutions to $x^2-y^2=a$ over a finite field.

Question

Let $F=\mathbb{F}_{q}$ be a finite field where $q$ is an odd prime power. Fix $a\in F\setminus\{0\}$. I would like to find out the number of solutions to the equation $$x^2-y^2=a.$$

Could anyone give any hints?

Thanks