Functional Testing Question:

Functional Testing sometimes called black box testing because no knowledge of the internal logic of the system is used to develop testcases.for example ,if a certain function key should produce a specific result when pressed, a functional tet validates this expectation by pressing the function key and observing the result.when conducting functional tests, you will use validation techniques almost exclusively.
Functional testing advantages:
simulates actual system usage.
makes no system structure assumptions.

Disadvantages
Potential of missing logical errors in software
possibility of redundant testing.

Functionality Testing:
Its part of Functional testing. Giving the input and checking the output. Testing the application against specifications.