Phal: how am I doing?

[Sibyla]

Hi there, I got a lovely Phalaenopsis from my mom, but I haven't taken care of any flower so far and she gave me an orchid, wow! Eventhough Phalaenopsis are said to be the easiest of orchids, I am afraid of its health. I am a bit afraid of the roots, most of the pics I saw are with green tips and mine seem to be fading away... and one small leaf that grows beneath another bigger is turning yellow. What should I do? I have no idea about how to find if I am watering it enough, the transparent pot stands on a few pabbles to gain the huminidity and not stand in the water.