The first question we need to ask is whether you are actually required to file U.S. tax returns. Generally speaking, U.S. citizens and Green Card holders are required to file U.S. tax returns regardless of where they live. Therefore Americans living in Canada, whether they have recently moved to Canada, or have been in the country their entire lives, are required to file U.S. tax returns, in addition to their regular Canadian tax returns.
Once you have established that you are required to file U.S. tax returns, the next step will be to assess your actual filing requirements. Please keep current with US/Canada tax law changes as they can significantly affect your annual filing requirements.
What forms need to be filed?
Assuming you are above the required income filing threshold, you will need to complete Form 1040 for the current year. The 1040 is the general income tax form, and is really only 2 pages long. The bulk of your annual U.S. income tax filings will be comprised of additional forms and schedules.