This is a very broad question. In terms of definition an autobiography is a nonfiction piece of writing which is written by a person regarding his or her own life and experiences.
In terms of comprehension, I would say that an autobiography is a nice blend of fictional and non-fictional elements. While this genre is classified as nonfiction, it has numerous elements of fiction. For instance, autobiographies have characters, plot, setting, mood and tone. These elements have to be analyzed in order to understand the autobiography.
In general an autobiography, like any other type of writing, can be analyzed be its authenticity, theme, and benefit to humankind.
An autobiography has some prerequisites in order to qualify as a work chronicling the life histroy of the writer.
It has a first person narrative, that is a type of prose which is written in a way that the writer is the protagonist, telling his story by himself in first person. For instance, the novel Great Expectaions, Moll Flanders etc.
It should dwell on the real events of writer's life, rather than being an escapist or romantic piece of literatue. Afterall real stories can't be like a fantasy prose fiction eg. Lord of the Ring!