Read Gary Johnson's excellent seven page overview of The Western from the online magazine, Imagesjournal. As you read jot down some of the article's key points so you can use them later when examining how John Ford's "Stagecoach" fits within conventions of the Western genre. It's important that you make your reading active by noting down important ideas and concepts from key paragraphs and also writing down questions of your own that you might wish to clarify by investigating further.
Don't rely on Internet research only. Remember hard copy magazines and books. An old tutor of mine, Brian Spittles, wrote a book on John Ford. It's called "John Ford (On Directors)". It would pay to see if your local library could find and lend this to you. Then focus on genre and John Ford as an auteur in "Stagecoach".
"Stylistically Ford was instrumental in developing new camera techniques, atmospheric lighting and diverse narrative devices. Thematically, long before it became conventional wisdom, Ford was exploring issues that concern us today, such as gender, race, the treatment of ethnic minorities and social outcasts, the nature of history and the relationship of myth and reality. For all these reasons, John Ford the man and his films reward thought and study, both for the general reader and the academic student. Ford's pictures express the world in which they were made, and have contributed to making what Hollywood is today. "