All of these assume no further reaction, and this nearly always is a poor assumption! Also, x stand for the molar solubility of the substance.

Dissociation Equation	Ksp expression	Ksp in terms of x
AgCl Ag+ + Cl-	Ksp = [Ag+][Cl-]	Ksp = x2
PbCl2 Pb2+ + 2 Cl-	Ksp = [Pb2+ ][Cl-]2	Ksp = x(2x)2 = 4x3
Al(OH)3 Al3++ 3OH-	Ksp = [Al3+ ][OH-]3	Ksp = x(3x)3 = 27x4
Fe2S3 2Fe3+ 3S2-	Ksp = [Fe3+ ]2[S2-]3	Ksp =(2x)2(3x)3 =108x5

There are two problem categories: given molar solubility, find K_sp, and given K_sp, find molar solubility.