We know and can explain "HOW" stuff works but can anyone answer "WHY"?

The why would come down to the laws of nature

why and how are different.

in biology, no one is able to answer why, but able to answer how.

why do we have two kidneys? no one can answer
how does the kidneys work? that can be answered.

anyway, the above may not answer your question.
well, put it this way. why do we have two kidneys is different from what is the biological significance of having two kidneys

That is philosophy

In some cases, we can answer why questions.

Why something works like that is because that is the way it was designed/developed.

Most "stuff" works out of necessity, that great mother of invention.

I do not understand the difference: We know 'How' a pedal cycle makes forward motion and on the same principal we know 'Why'. In both cases it is by someone pedaling. That is why it goes forward and also how it does.