Once your contacts receive your email and click on the widget link, they will arrive at this special sign-in page, specifically for that title.
There they can sign in with their existing NetGalley account, or if they are new to NetGalley, they can register for an account right on that same page.
After signing in, they are immediately taken to the Title Details Page for that book--no requesting and no waiting to be approved, since you have pre-approved them with the widget -- and download the title to their reading device.
If you would like to help your readers understand how to use a widget to view a title, send them this link.