Minecraft wiki entry for Brewing_Stand, associated text: They accept brewing ingredients from hoppers pointing down into the top.
Any valid potion recipe can be preloaded for "hands-free" brewing of a complex recipe, with the nether wart falling through into the stand for the first step.
Bottles and fuel are accepted from hoppers pointing into the side.
Finished products can be pulled out by hoppers below, but each stage of brewing counts as a batch of "finished" potions.