Point of View
If you want to write nonfiction, you must know about the different points of view at your disposal, especially since some nonfiction genres are written in one point of view while others must be written from a different point of view.
You must be able to control the point of view. Shifting from one point of view to another betrays the consistency of the narrative voice and can confuse the reader. Shifting points of view are rarely used in nonfiction and when this does occur, it is generally limited to books and employed by experienced writers.
The Four Points of View
There are four points of view from which you can choose to write: the first person, the second person, the third person omniscient and the third person objective. When writing in the first person, you are speaking directly to the reader and frequently use the word I. In the first person, you'll be conveying information that only you would possess. Typically, personal essays and memoirs are written in the first person.
Writing in the second person is an even more direct way to address the reader and commonly employs the words you and yours. How-to/self-help books and manuals are often written in the second person. This book is written in the second person.
The two remaining points of view are written in the third person. The third person omniscient is where the writer knows everything there is to know — like a mythical Greek god with an “all-seeing eye.” Indeed, the writer can even enter the minds of the subjects in the work. For example, in a biography about Abraham Lincoln that is written in the third person omniscient, the reader may actually get a view inside Lincoln's head and experience what he is thinking. The third person objective does not have this capacity but describes things as they are seen from the outside. So in a biography about Lincoln written in the third person objective, the reader will not have access to Lincoln's thoughts.
Whether intended or not, once you use the I word, you will have shifted from whatever point of view you had been utilizing to the first person point of view. This should only be done if this is your intention, so take care not to use the I word unless you have been writing in the first person.