Though the same source plant is used, the different regular teas are made by using different processes. Green tea is not fermented, Woolong tea is partially fermented, black tea is fully fermented, and Pu-erh tea is post-fermented. This means Pu-erh tea’s processing includes both fermentation and then prolonged storage, or “aging,” under high humidity. Pu-erh tea that is aged for a longer period of time is supposed to taste better.
Green Tea is fresh, bitter and better to drink it in spring, summer. It's good for cleansing but may upset your stomach and better not to drink with empty stomach.