How to write this Ksp Expression

My problem says to write the Ksp expression for the equation:

Ag2SO4 (double arrows) 2Ag^+(aq) + SO4^2-(aq)

I don't understand what Ksp means or how to apply it to this problem. Can someone please help??

The Ksp expression is:

Ksp = [Ag^+]^2 [SO4^2-]

A varieyy of Ksp problems here:

http://www.chemteam.info/Equilibrium/Equ…