Orchards, like fields and ranches, are special buildings that can be used to plant, grow fruit trees and produce various fruit.
Orchards can vary in size. When placing them, you decide how large an area a single orchard will cover. Larger area means more produce and it is always a good strategy to maximize the size of an orchard, but it's not always possible.
Dependency on soil fertility
An orchard's efficiency, meaning how much it produce in a year, directly depends on soil fertility. If you turn on the soil fertility grid, you be able to clearly see where the soil is good and where it's bad. Better fertility, naturally provides greater yields.
Choosing the fruit
Different fruit types are used for different things. Some are used purely as food, which works great to boost food variety, an important part of each citizen's health. At the same time, some fruits can be further processed and used in the production of other, more advanced resources. For example, grapevine is used to produce wine, a Gentry luxury.
To choose what fruit is planted in an orchard, use the dropdown control on the orchard's info panel.
It takes time
Don't forget that it takes time for an orchard to actually start providing fruit. The minimum is one whole year after the orchard is planted. If you wish to change what is grown, do it on the info panel, but you will have to wait for the orchard to first be harvested, then chopped down and re-planted with the new chosen fruit.