There are many species of Orchids (~28,000), and innumerably more hybrids and cultivars.
However, if one were to randomly buy an orchid in an American supermarket, chances are it would be a Moth Orchid (Phalaenopsis hybrids). There are several reasons for this. They are attractive, long-blooming, of easy care, and grow well in moderate light, even the light in a north-facing window is often sufficient.
What follows is care for most Phalaenopsis, if you do get another type of orchid the care may or may not be different.
Phalaenopsis do best with either filtered sun or bright indirect light. They are grown in loose, fast-draining media, often coarse, bark, sometimes sphagnum moss, scoria, or expanded shale. The media should be allowed to partly dry before the next irrigation.
Fertilize monthly with a complete, liquid fertilizer.
As you can see, the day-to-day care of a Moth Orchid is not very different from that of an average house plant.
The biggest difference comes when it is time to re-pot, as special media is required instead of potting soil..