How we know the "Real or True"...

'Air' is a vital element of every human being and its exist in our saroundings its true. We can't see the Air but we can feel and when we get breath. From the Childhood I knew Air is existing and at first I knew it from my book when I was school student. Teacher said us the factor and he gave us some example about Kite flying, Bird to make us understood and he said these all are happening because of Air. Then we easily understand that Air is existing our saroundings...