Unless you are using hydroponics, all of your plants will grow in some sort of soil. The better we understand our soil, the easier it will be for us to take good care of it (and easier is good).
Soil tends to form layers on top of bedrock. These layers of soil are called horizons. Just above the bedrock is a layer of unbroken rock. There are generally no plant roots here. This is called the regolith.
There are four basic soil horizons:
All of this normally sits on top of a hard layer of solid bedrock. The U.S. Department of Agriculture has an amazing interactive map that can help you learn more about your local soil.
Artificially and naturally occurring layers of impenetrable hardpan can thwart even the vest gardeners.
The best way to understand your soil is with a lab-based soil test.
You can grow a surprising amount of food in your own yard. Ask me how!