Sheng Pu-erh starts off life at a low oxidation, around the same of green tea around 5%. During processing the oxidation is not entirely stopped, so as it ages it becomes more oxidized until eventually it becomes fully oxidized.

Shou Pu-erh gets heavily oxidized during its processing, leaving it closer to black tea oxidation levels by the time it is done. Oxidation does slowly continue as Shou Pu-erh ages as well.

Sheng Pu-erh is prepared mostly the same as a normal green tea, although green tea is cooked at around twice the temperature than Sheng Pu-erh. This category is often left to age in varying conditions for many years to develop a deep and earthy flavor. 

Shou Pu-erh is prepared in a way that is more similar to composting, where the leaves are gathered up in a large pile, given moisture, and tossed occasionally in order to encourage the growth of micro-organisms that produce similar tastes to aged Sheng Pu-erh without going through the long process of natural aging. 

Pu-erh was originally developed to be standardized as a trade commodity. It originated in Yunnan provence in China, and is still made there from large leaf tea plants - many of which are very old. Many of China's neighbors traded for tea, so they needed to make it easier to transport and regulate. In order to make a usable trade piece, the Chinese government developed large stones that would press a set amount of leaves into a bing or cake. Seven of these cakes would then be stacked into a tong, which is both the name of the stack of cakes as well as the basket they are carried in. These would then be traded with China's neighbors for the local commodities, one of the most famous being horses.