"A black hole grows as gas from space flows onto it. It then releases two kinds of energy from that gas: radiation energy in the form of photons and kinetic energy in the form of wind jets. The more matter falls in, the more energy is released."

"The black hole can be a fussy eater: instead of swallowing all of the material, it sometimes pushes a fraction of it away in the form of two powerful jets of particles. Because these jets release mass and energy into the surroundings, the black hole has less material to feed on."

The quotes above are from an article from the AAAS and an article from Science News. They both do a good job in explaining where the Black Hole jets come from.

http://www.aaas.org/news/science-black-holes-emit-surprisingly-strong-jets

http://www.sci-news.com/astronomy/science-black-hole-jets-01543.html

Here is a video of an illustrated model of a black hole in a binary system. We see the black hole because it is devouring material from the companion star.

http://www.nasa.gov/mission_pages/swift/bursts/devoured-star.html

Black Hole Eats Star, Beams Signal to Earth