Questions

An autobiography- is when you get to tell your own story.  Autobiography's are usually written in a book, but can really be expressed in any way, even through words.
A self-protrait is either an image or a picture of the the artist created by the artist. The person takes or draws the picture themself.

In both an autobiography and a self-portrait, you can reveal as much or as little as you please.  Some people choose simply to confront the camera with little or nothing else in the picture. You get to pick the setting.

An autobiography is expressed in words, the person tells you about there life. A self-portrait is expressed through a picture or a painting, the artist shows you things about them rather then telling you like in a autobiography.