To create a new document in either Photoshop or PSE:
1. Either click on "File - New - Blank File" or use the keyboard short cut of Ctrl-N (or Command-N for Mac) to open the new file dialog box.
In the New document box, click on the Preset to choose your paper size (Scrapbooking for 12x12, US Paper for 8.5x11, various photo sizes, or choose custom to set your own size).
Decide whether you want to measure your document in inches (or cm) or in pixels and set those drop-downs appropriately.
Make sure the Resolution is set to 300 Pixels/inch (or 72 for web-sized images); that the Color Mode is set to RGB Color and the Background Color is set to White (or Transparent).
Click OK to finish & begin work on your new document.