Make sure the photos are big enough
For best results, you'll want to use images that have as many pixels as possible. If you use tiny, 1-megapixel camera phone photos on a wall calendar, you probably won't like the results. But any digital camera capable of capturing 3 megapixels or more should give you good picture quality. Since most calendars present pictures at around 8 by 10 inches, photos taken at a minimum of 1600 by 2000 pixels will get you off to a good start. There's no harm in uploading photos shot at even higher resolutions.
After your photos are organized, upload them and use the site's tools to lay out your calendar. If you have the option, customize the calendar with important dates (birthdays, anniversaries, and so on). Then order enough copies for everyone on your holiday shopping list; the site will have them professionally printed and mailed to you, or you can arrange to send them directly to your recipients.