Will upvote
in a brief paragraph of about 150 words, discuss memoir. what is a memoir, and what is its
purpose? which kinds of stories are best for a memoir and why?

A memoir is something written about a specific topic based on the knowledge you know personally or gather from specific sources. 
The stories in one would have to depend on what the memoir is about. Should the memoir be about your best friend, you'd write all of the things that made them who they are today. Should the memoir be about an ancient warship, you'd write about what happened to the warship and what wars it was in. As long as you correctly citate your sources

A memoir is like something about your background history (ithink)