All tea comes from the Camellia Sinensis plant. The difference is in how much the leaves are oxidized and processed after they have been plucked. During the oxidation process the leaves undergo chemical reactions that result in the variations of taste and colour. Heating stops the oxidation process.
There are 4 main types of tea:
Green tea may be rolled or processed and then heated quickly to stop oxidization before it truly begins to happen.
White tea is left to oxidize for a very short period before heating. White tea is usually not processed at all.
Oolong tea is partially oxidized and has some of the characteristics of both green and black tea. Oolong leaves may be rolled or twisted. Oolong are very aromatic and full of flavour.
Black tea is the most common type of tea in North America. It is fully oxidized and results in a full rich flavour and amber liquor.
Herbal teas are not made from the Camellia Sinensis plant but are infusions of herbs, leaves, flowers, fruit or other plants.