Your first step in composing your analysis of "A Piece of Steak" by Jack London is carefully reading over your assignment prompt to understand what sort of analysis your instructor wants to see. An analysis is not a summary, simply giving a short version of the content of a story. Instead, you can do a literary analysis which examines the literary devices in a story or a thematic analysis which focuses on certain aspects of the content, plot, or situation.
One theme you might analyze in this story is that of the strength of youth as opposed to the wisdom of age. In the story, this theme is presented as universal. All boxers begin their careers as young and strong, and next develop skills to go along with that physical strength, and then their bodies grows weaker, to the point where their skills and experience can no longer compensate. Unfortunately, by the time Tom comes to understand this, and by the time he comes to understand that his younger self's choice of a career as a boxer was due to ignorance of this, it is too late. From a Marxist point of view, you could argue that it is only at the end of the story that Tom realizes his complicity in a system of oppression that makes the destruction of the bodies of the poor a form of entertainment.