The Common Criteria in the simplest form works to answer two distinct questions.
What are they?

A.
What does the product do and how sure are you of it?

B.
What security mechanisms are in place and how reliable are they?

C.
Do other products exist like this one and which is better?

D.
How trustworthy is the manufacturer and what other products do they make?

Explanation:
The Common Criteria (as well as other evaluation rating systems) work
to answer two basic questions: What the security mechanisms within the product do,
which determines its security functionality; and how sure are you of it, which
determines assurance.