Look in your community for opportunities to attend small business classes, marketing classes, horticulture classes or working in a greenhouse with a master gardener. Look online for videos, books, blogs, or guides that describe the daily goings on inside a greenhouse.
Lastly, learn by doing! Start smallscale, in your own backyard. Make sure that you have your own experience with your hands in the dirt that you can use as a point of reference later on.