You can forage the tea, or get it from critters. once you have completed the quest for learning taelosian brewing, just go to a brew barrel and put the tea in. Yeild is one to three, changing the tea from the green leafy appearance to a small pouch. The tea is then used in brewing some excellent recipes.
White tea is tea and flavorings like mint or ginseng. Black tea is mouldy tea leaves, tea and the flavorings. Green tea is handfull of twings and leaves, tea, and with flavorings. Also, you can make the plain tea. black, green or white, without flavorings. Gives nice stat boosts. I have sold the end product in bazaar for 5 gp per tea.