When most Americans think of tea, their first thought is iced tea. Depending on where they live, their second thought is usually either sweet, or unsweet. Of course, there is a little more to it than that.
There are several types of tea, and also several steeped beverages that are called "tea", but really aren't tea at all.
White, yellow, green, oolong and black tea all come from the Camellia sinensis plant. Properly speaking, tea is an infusion of the leaves of Camellia sinensis. An infusion of leaves (or stems, roots, flowers) from any other plant such as Rooibos, herbals, yerba mate etc. is a tisane.
Type: Theoretically, you could produce any of the types of tea from the same tea plant. The final product is determined by the cultivating practices, harvest method, oxidation and drying methods. All of the variables result in subtle, and not-so-subtle differences in the flavor, aroma and appearance of the tea.
Cultivar: There are two basic varieties of Camellia sinensis and they are: Camellia sinensis var. sinensis, and Camellia sinensis var. assamica. Very basically, the former is the tea plant native to China, which has smaller leaves, and the latter is the tea plant native to India, which has larger leaves, and is the variety from which we get Assam tea. There are many cultivars within those two varieties that have been selected for traits desirable to the region they are grown in, or that produce a finished product with desirable qualities. Think of it like the practice of selective breeding that has produced the wide variance in dog breeds, or the rainbow array of heirloom tomatoes.
Origin: Terms such as Ceylon, Darjeeling, Kenya, and Formosa, refer to where the tea was grown. Climate and soil can have a big impact on the flavor of the teas grown in a region.
Process: There are two basic types of harvesting, Orthodox and CTC (cut, torn, curled). Orthodox is harvested by hand, and CTC is harvested by machine. If your loose tea looks like dried, twisted leaves, it is probably an Orthodox tea. If your tea could visually pass for instant coffee (Yorkshire Harrogate and Irish Breakfast for example), it is probably CTC.
Blends: "Breakfast" "Afternoon" and "Evening" teas, as well as many iced teas and teas with British-sounding names, are usually tea blends. Often, the tea from one estate might have some particularly good flavor traits, but be lacking in another area(s). This could be due to a stressful growing season, or may simply be a characteristic of the soil and climate in that region. This tea might be blended with tea from other estates or other parts of the world to create a more balanced flavor. This is how some brands of tea achieve a consistent flavor from year to year.
Many tea connoisseurs choose to drink single-source teas, evaluating each tea on its' own merits. After much practice, they develop their palates to the point that they can detect subtle variances in flavor, and can even tell where a tea originated. You don't have to be a connoisseur to appreciate and enjoy drinking good tea. I'm certainly not.
There are some general rules of thumb for preparing the different teas and tisanes, but they are just a starting point. You get to decide what a good cup of tea is to you. There is no one right way, so don't let anybody try to convince you differently.
Some people will be eternally happy with their favorite brand of tea bags, and others will be equally happy exploring the varied world of tea. Most of us fall somewhere in between.