What is a "variety" of a plant, say a radish? It is a type of radish. A particular variety may grow better in your area, as well as having characteristics that you like, such as a certain taste or look. Seeds may also be "heritage" seeds or may be those developed by man to have special characteristics (but only for a single season) such as "hybrid" seeds. Check the "Seeds of Diversity" website for more about heritage seeds and their value: http://www.seeds.ca/
Knowledgeable gardeners in our area such as Dave Havard and Tracy Strong have compiled lists of preferred seed varieties to grow here. Gardeners at our community garden invite you to join with us in developing a list of varieties and plants to grow in our area. What you can grow will depend on your "micro climate" and growing conditions. These vary around the area, and even from plot to plot within our community garden.
Seed catalogs provided by companies such as Vesseys, Stokes, Dominion, Lindenberg and Saltspring Seeds provide a selection of seeds and plants to order, and often provide growing requirements and information for each plant. Ordering seeds allows more control over variety than just shopping at local stores does. Seeds stocked in local stores include varieties that are selected for other areas with growing conditions different from ours.