Types of Tea
All tea comes from the Camellia Sinensis plant, native to southwestern China. There are two main variations, Camellia Sinensis sinensis and Camellia Sinensis assamica. The leaves are harvested at various stages of development but the processing is what really determines the type of tea (green, black, etc).
"Herbal teas" are not really tea but, since they are prepared in a similar manner (soaked in water for a time), they get lumped in the same category. Another word often used is tisane (which you may have seen around) but most people just call it herbal tea because how do you even pronounce that other word?
There are several different types of "real" tea: white, green, matcha, oolong, black, and pu-erh. It's basically the oxidation level in the dried leaves that makes the different types.
The most delicate of the teas. Not as popular due to its rarity.
White tea often consists of the leaf buds and/or newly unfurled leaves. The leaves are then withered (basically set out to dry) and completely dried in a highly controlled manner with no oxidation. These teas are rarely shaped.
After the leaves are picked, they may (or may not) be withered and then "cooked" to stop the oxidation. There are two main ways of stopping this oxidation: steaming or roasted (oven-fired, wok-fired, etc). Chinese green teas are often fried while Japanese green teas are usually steamed. After cooking, the leaves go through a shaping process. This is how you get the various shapes of green tea (gunpowder balls, wirey, flat, etc.) and can either be done by hand or machine. After shaping, they are dried again before packaging.
Current matcha preparation was developed in Japan. The tea bushes are shaded for a few weeks before harvesting to increase the chlorophyll (chlorophyll? More like borophyll) count. Then they only pick the finest leaves. You can prepare the leaves like regular tea, at which point it gets called gyokuro, or you can grind it into a fine powder to get matcha.
There are different levels of matcha which will depend on how involved the process is. Culinary/Food grade is the cheapest and best suited to cooking and mixing. Then you have more premium/ceremonial grade (used for a pure tea drink) where they use only the finest leaf buds, and mill it slowly so it doesn't heat up the leaves which will affect the taste.
This is where you get a lot of variation in flavor because the leaves are oxidized between 10 and 85 percent before they are "cooked" and shaped. Some will be more like green tea while others more like a black tea, all depending on the tea master's preference.
Green tea is more popular in eastern countries but, due to the extensive traveling required to get it over to the western countries (ie England), black teas became the popular option in the west since the fully oxidized leaves did not go bad as quickly. They are often withered and allowed to fully oxidize before they are shaped.
This is a less popular tea as the taste may take some getting used to. This tea will actually go through a fermentation process that gives it a strong, earthy, almost musty flavor. There are two different types: Raw (sheng) and Ripe (shou). Both start out being processed similar to green teas where they are "cooked" and shaped, but then raw pu-erh is often pressed into cakes where they will ferment and continue to oxidize. They will continue to oxidize and ferment for years with the taste changing throughout. Ripe pu-erh is actually processed akin to composting where they carefully control the moisture and heat that accelerates the fermenting process.