Rooibos, or Red tea is not actually tea, (Camellia sinensis) but comes from an evergreen shrub (Aspalathus linearis) which is native to the Cederberg, Western Cape Province of South Africa.
How is it processed: The leaves are picked, oxidized and dried, similarly to black tea. The oxidation process gives the Rooibos its' characteristic reddish-orange color. Green rooibos, where the oxidation process is skipped, is also available, and as you might guess, the processing is similar to green tea.
What does it taste like? I have seen rooibos described as nutty, earthy, neutral, and even tobacco-like. I would agree with the characterization of nutty and neutral. I don't find the unflavored rooibos to be exciting by itself, but it plays very well with other flavors. When blended with nuts, fruits or florals, Rooibos really shines. I am particularly fond of the Berries and Blossoms and Marzipan flavors that I offer, but so far, I have not yet tried a flavored Rooibos that I didn't like.
How do I prepare it? Just as you would prepare black tea, but you can wander off and forget what you were doing, without coming back to a bitter cup. Not that you would ever do that. You can drink it hot, or iced, or made into popsicles. You can add milk, or sugar, or honey, or Stevia, or just drink it straight. One thing to consider though, Rooibos is smaller than most loose teas, so you'll need an infuser with very fine mesh.
What are the known or perceived health benefits? Rooibos is high in antioxidants--and like tea, the green variety is higher than the fermented variety. Rooibos does not contain caffeine, oxalic acid or sulfites. It is also low in tannins.
Any risks? I am not aware of any health risks associated with rooibos tea.