Although the above answer is mostly correct, it would be more appropriate to say that the book is made up of vignettes (pronounced vin-yets, the g is silent).
Vignettes are different from short stories in that the they are not complete, do not have a clear begining, middle, and end, fully developed characters, a plot, etc... They are better viewed as snapshots, or word pictures, that capture a particular subject, person, or memory. Esperanza gives us a big picture of her life by providing these smaller snapshots. They together form a cohesive whole.
hmm...I'm not entirely sure what you mean by what type of book, but it's a fiction book of short stories, that first appeared in 1983. There are 44 short stories that evoke the circumstances and conditions of a Hispanic American ghetto in Chicago. The narrative is seen through the eyes of Esperanza Cordero, an adolescent girl coming of age.
Well, if you want to know the genre, i speculate that this book is a coming-of-age type. Over the lapse of year(almost), Esperanza narrates vignettes (as mentioned in cnorth answer) of that period of time.