All teas, regardless if its white, green, oolong, black all come from the Camellia Sinensis plant.
It is the processing methods that creates different kinds of teas. In general, the more oxidized the tea is, the darker the colour would be, and also the higher the level of caffeine as well.
Black teas go through a much more complex and lengthy processing. For Pu-erh teas, the teas get oxidized and then is fermented as a second process again.
Oolong teas are generally half oxidized, producing a variation of strengths for this type of tea.
Most teas go through a process from plucking, withering, rolling, oxidation and then drying.