For example, if you hold the phone upright and take a photo, so the photo is vertical or portrait, then the actual image file is technically horizontal, as all photos are "sideways", (think of a 4x6 photo coming out of the printer), you would need to turn the photo right side up to view it vertically. This is the same with a digital photo. When you view on a computer, or upload, you may see the image sideways. If so, then would then need to rotate the image using your photo viewing or editing software.
After the image is rotated, then you can upload it and it will appear correctly. This may vary based on your computer software, browser and/or camera.
See this link for more details:
Rotating photos in Windows 7 or prior using Windows Photo Viewer:
Apple Macintosh OSX:
LinkU also recommends this free photo editor if you need one, which you can download here:
You can also use most other photo software or editors to rotate your photos and search Google for instructions for your specific photo software or operating system.