Var(ε) = E(ε2)

I have no idea how this equation works. Can someone pls help?

Var(ε)=E[(E(ε)-ε)2]=E[E(ε)2-2*E(ε)ε+ε2],E(ε)2=0,2E(ε)*ε=0,so Var(ε) = E(ε2).