Size chart is available in the images. The fit of the slide is pretty exact (a little too exact). Most order 1 size up for comfort/growth.
If you don't see your "theme" or have a unique idea, select "Other".
When specifying details for the design, be sure to include everything applicable: Color (s), Name, Number, etc. If you have a logo, you will need to forward your email confirmation to firstname.lastname@example.org and attach it to the email.