I thought it may be a good idea to reiterate some earlier stuff on orchid growing as I believe that many beginners think that orchids grow in a similar way to other house plants, this is a misconception and will undoubtedly lead to problems growing these unusual plants.
The first picture shows a phalaenopsis orchid growing in its natural habitat and the second growing in my bathroom. Aerial roots can clearly be seen on the first photograph where the orchid is growing on a tree branch in the tropical biosphere at The Eden Project.

My orchid is growing in a bark medium which simulates the bark of the tree, which they grow on in the wild. On the right of picture 2 is a flower spike in bud and on the left a keiki or plantlet with its own flower spike. Eventually this plantlet will grow aerial roots and become a separate plant.

Orchids are parasitic and derive some of their water and nutrients from the host plant, which is why you need to simulate these conditions carefully in order to grow them successfully.