The Four Basic Teas

The four basic teas are:

Black tea is processed using oxygen (oxidation) . When tea leaves are oxidized, they change in color and flavor.  Black tea is the strongest brew because it is oxidized the longest.

Green tea is not oxidized or fermented at all, which gives it a delicate, pungent flavor.  Green tea leaves are steamed, rolled, then dried.

Oolong tea is made from partially fermented leaves, which gives it a flavor somewhere between black and green tea.  It is processed using oxygen (oxidation). When the leaves are oxidized, they change in color and flavor. 

Wite tea is more rare than black, green or oolong, and it is thus more expensive.  White tea, made from the same plant as the others, is simply made from leaves that are harvested before they're fully open.  It has a light, sweet flavor.