Answer:
Sympathy is something you can feel and express because you've been through the same experiences as the person you are sympathizing with, e.g. I felt sympathy for my friend when her father died as my dad died a few months ago.
Empathy is the ability to imagine what it must be like for someone to be in a difficult situation even though you've never experienced that situation personally, e.g. While my father is still alive, I empathized with my friend whose father died recently.