Actually, the tea tree's leaves and the coffee plant's leaves look somewhat similar, only the tea leaves are smaller. Black tea undergoes a complete fermentation process. Leaves are picked, left to wither slightly, then they are rolled. Internal enzymes cause fermentation. The tea is then sorted and packaged.
Oolong tea is semi-fermented tea, produced with larger leaves.
The fermentation process is stopped by firing the tea earlier than black tea. Green tea is produced by steaming the leaves right away, thus destroying the enzymes that would begin the fermentation process. The tea is then dried in the sun, fired, sorted and packaged. Herbal teas aren't really teas. Instead, they are herbal tinctures.