I'm still confused about the difference between these two concepts. Could you explain it with some examples? Thank you in advance!:)
They are special terminology from the Y model.
DS | (overt movement) SS / | (covert movement) PF LF
Today it is more common to draw a kind of T model.
| | LF __SO__ PF
No Deep Structure (DS) in the T model. Surface Structure is nowadays called Spell-out and is rather a point in the derivation (a point in time) than a representational level. There is "before" and "after Spell-out" rather than "at Surface Structure".