FUNCTIONAL TESTING:

 Testing a product functionality is to test whether the work of that functionality if finished as required and we don't check how fast the work is finished and how economically work is done only we concentrate on its behaviour check.

FOR EXAMPLE:
we are purchasing any vehicle, we will check for its general functions like its Headlights are switching from gold light to white light when its switches are ON and OFF mode, indicators working properly.

whether brakes are operating properly, stand is working good, accelerators are fixed good enough, its speedometers etc.

If we check its milage per litre of fuel, then it comes under non-functional testing.

NON-FUNCTIONAL TESTING:

In non-functional testing we check its performance that is the, whatever functionality it might be. How time saving and how cost-effective will be our checking perspective.

FOR EXAMPLE:
Two coders, coder A and coder B having a program of their own creation each for a same functionality, both getting same data from the user and giving same output as user required.

But coder A's code is giving output in 2 minutes aft running the code whereas coder B's code is fetching output in 1 minute, so it is clear that code of coder B is time saving and hence cost effective as it has less lines of codes to execute compared to other. In this case non-functional testing technique has taken place to identify best code.

In other cases, like public use websites, we check its behaviour in certain conditions as how fast it is loading each page when more users try to use that web page at a time, and it fits in all kinds of browsers.