The Form 1040 is the master income tax form.
All other documents, schedules, and worksheets ultimately flow into the Form 1040.
For a schematic description of what is really going on in the 1040, see here.
For quick reference to see what's what on the 1040, click on the images below to enlarge:
Here is a color-coded Form 1040 that shows where you will find the various different
types of income items, above-the-line subtractions, below-the-line subtractions,
non-refundable credits, and refundable credits.