Pick a subject for your documentary. As it is your senior year, you'll have a lot of topics to choose from. You could try making a film that encompasses your entire academic career. Touch on key events and milestones that affected you and your classmates. Or you may want to focus on just one particular important event. For example, maybe your basketball team won the state championship or your school hosted a community-wide yard sale.
Grab a video camera. Considering the fact that you are in school, you probably want the cheapest camera you can find. You can purchase your own video or high definition camera for around $200.
Shoot all the footage you could possibly need and then shoot for 10 more minutes. Documentaries are differenct as they tell true stories using real people and real resources. Interview everyone who could have something relevant to say on your topic. Shoot all the footage you can of anything having to do with your topic; the more you have, the better.
Edit your raw footage down to the desired length. Assemble your footage in a way that best tells your story. Inter-cut your interviews and your raw footage so that it catches the eye of your viewers and keeps them entertained.
Add your credits. Credits are going to be either at the beginning of a movie or the end. Whichever you choose, be sure to include the names of everyone who assisted you on your film. Whether they held a microphone or helped you set up an interview, thank them in your credits.