When you need to solve a question such as this one, the tool that could help you the most is a dictionary - an alphabetically arranged listing of words, which gives us different information about those words, such as their definitions, usage, origin, pronunciation, etc.
These are the differences between the listed words:
When something is uncomplicated, it's simple (the opposite of complicated) or straightforward.
When something is simplistic, it's oversimplified. When something is simplified, it's made in a way that is simpler or easier to do or understand.
When something is comprehensible, it's intelligible, able to be comprehended or understood.
