Check out the chapter on fertilizing in Ortho's
All About Orchids or any other decent book on orchid culture. Fertilizing, how, what, when is subject to 1) what kind of orchid you have - there is no one approach that applies to all orchids, 2) the conditions underwhich the plants are being grown, and 3) the habits and preferences of the grower.
There are
different approsches to fertilizing outlined in a different thread.