I need HELP! Project due TODAY.

I need HELP! I am creating form in which a date range is requested in the form. I went in to properties of that field and selected "Custom" under "Date" under "Format" and entered "mm/dd/yy to mm/dd/yy". In the example field, it's showing up as "mm/dd/yy ao mm/dd/yy". Also, when I preview the field, even if I place the date in as set up in the settings, a dialog box pops up and tells me I'm entering wrong. Can someone tell me what I'm doing wrong!? Also, how can I get the "mm/dd/yy to mm/dd/yy" to show up in the field so the user doesn't have to guess to start???