Expand and Simplify

What is the different between Expand and Simplify ?

Crudely speaking, they are opposites:

In[1]:= Expand[(x + y)^2]

Out[1]= x^2 + 2 x y + y^2

In[2]:= Simplify[%]

Out[2]= (x + y)^2

Ooh sorry I want the different between Simplify and Factor not simplify and expand ,Because I get the same result