Once you've completed the previous steps in this tutorial, you should have measurements for both length and width of each of your feet. You're going to want to use the larger of each of these measurements in determining your final shoe size.
For example, if your left foot is 1/4 of an inch longer, then use your left foot's length measurement. If your right foot is slightly wider, then you'll use that number for your width.
After you've come up with your two biggest numbers (length and width) you'll want to subtract 3/16 of an inch from each of them. This is to accommodate for the slight space between your actual foot and the line made by the pencil.
These final numbers are your actual foot measurements, you can convert them to the appropriate size and width using the links below, but again, I want to emphasize that these (or any) shoe size charts are not going to give results that are as accurate as you'd get by visiting a shoe store and having your feet measured by a professional.
Women's Shoes Width and Size Charts
Men's Shoes Width and Size Charts