If you want to learn more, Haliburton put together a nice site with an animated video to give a broad overview of hydraulic fracturing without a lot of in depth detail.
http://www.halliburton.com/public/projects/pubsdata/hydraulic_fracturing/fracturing_101.html
Halliburton is an excellent resource.
They were my customer in the 80’s as well as Noble Drilling, Cherokee, Schlumberger, Amerada Hess(I will always be grateful to Mr. Hess, who passed some years ago) Every oil company in Cushing, Drumright, Yale, most of Western Oklahoma except Bartlesville based Phillips.