Click "Create new"

Make sure units are "Inches" rather than "pixels."

Choose the size/layout of your page, though you can always change it later on if needed.

If you click "More Settings" before creating your document, you can make more specific adjustments.

The main one you should consider is Color Mode.

If you plan on printing your file, you should use CMYK.

If your file will only be digital, you can use RGB.