One thing which puzzles me is what is the explanation for kiwi bird's wings - they are so tiny and do not seem to have any use, or that could use it in future. How do you explain it best?
This question seems to imply that you expect all aspects of every creature to have a current, or future use. Why would you expect such a thing?
We have things in our own human bodies that are unrequired - like the human tail-bone. What's the use for us to have a tail bone? What's the future use? There is none, currently - and evolution doesn't "plan" for the future, it adapts to the present.
We have a tailbone because we evolved from mammals that used to have tails. It doesn't need a current or future use.
Same with the kiwi bird's wings. The kiwi bird has wings because it evolved from birds that used to have wings. It doesn't need a current or future use.
If you think a current or future use is required - that's simply an incorrect assumption about evolution and reality.