Why?

One of the main questions you have to ask your self is WHY do you want to do documentary photography, this mainly comes from the heart and what interests you, what moves you, and what you feel so strongly about you wanty ot stop it.

All of this will be covered later but for the moment watch this video from Witness.org by Peter Gabreil

Its quite moving, but there are also other points, a story can be easily denied, but pictures and video is much harder to deny. A further point is that the latest gear is also not needed.