This is one of the specialities and originated in Berlin or Hamburg. You can find all kind of varieties on this easy to make snack. German people eat it like burgers.
To make a currywurst you just need a grilled sausage, some ketchup and curry.
1. Grill the sausage
2. Put it on a small plate and cut it into small pieces.
3. Put Ketchup on top of the small pieces (some people also add mayonaise)
4. Now finish it with curry powder on the top.
I prefer to eat it with bread.
PS: Here is a video of a man making it (first he puts the grilled sausage in a machine, which cuts it in pieces).