This is a 3-part puzzle. Parts can be solved out of order, but, in the end, parts must be put together in order they appear (1, 2, 3) to solve the whole puzzle.
Parts are independent from each other. There is no need to combine pieces of different parts before every part is solved.
Every part contains a puzzle and its key. You'll have to figure out which is which.
The keys contain what has already been done.