Photosynth.net is host to two different image formats: photosynths and panoramas.
If you'll be using the Windows Phone or iPhone app, you'll only be able to make panoramas.
You can also use Microsoft ICE or Adobe Photoshop to create higher resolution panoramas to upload to your account here.
The most important factor, when shooting a panorama, is to try to keep your camera's lens as close to possible to the same exact place in the air, while looking in all directions. In other words, don't hold your camera at arms' length and swing your camera around you. Instead, rotate your body around the camera lens. Here's a quick little playlist on YouTube where several different panorama app tutorials all tell you this same tip. http://bit.ly/howtopano
The reason that it is important with panoramas for the camera lens to not move is so that closer objects will line up the same way with background objects in all of your photos.