You pick how you end up at a 1:3 ratio for a panoramic image. 2:3 (4x6) is the ratio for most SLRs while 3:4 is the out of camera ratio for point and shoots. The 1:3 ratio can be accomplished by stitching images together or by cropping it out of a single original image. The idea is to come up with a subject and composition that is best presented as a horizontal or vertical panoramic.
Helpful hints:
(1) If you are stitching multiple images together, study the composition, meter the light throughout the area, manually set the exposure that works best and then shoot the images that will be used to stitch the panorama.
(2) A level platform (tripod, wall, etc.) helps make the stitching process easier.
(3) Avoid using wide angles lens perspective (anything under 35mm is more challenging) to capture the multiple images because the edge distortion is more difficult to align.
(4) If you are cropping from a single image try to compose splitting the down the middle long way or at least think in those terms as you are capturing the image.
Let this be fun and challenging. I'm posting early Thursday to give extra time to think about it and execute (and because I have a wedding to shoot this weekend).
“Simply look with perceptive eyes at the world about you, and trust to your own reactions and convictions. Ask yourself: "Does this subject move me to feel, think and dream? Can I visualize a print - my own personal statement of what I feel and want to convey - from the subject before me?” -Ansel Adams

(link to guidelines if needed)
Scott (for Walter and Scott)