There are a few ways you can handle this.
Once they have registered as a user on your site, you can add them to levels in the WishList Member – Members area.
If you want them to receive the prep email, you would add them to any 12 Day Detox Group level and then you can set that group level in the Sequential Upgrader to move them to the 12 Day Detox Program level on a certain date in the future as the set up in the instructions are shown. If anyone else is in that same group they would also be moved on that date as well. You could even set it for the following day if you wish.
Or, if you want them to get the prep email and also have them start at day 1 of the program the same day, you can add them to a 12 Day Detox Group level and then add them to the 12 Day Detox Program level as well. You would then just remove them from the 12 Day Detox group level the follow day, so that that group level is empty for the next group you want to set up to upgrade on a specific date in the future.
Or, if you want them to start at day 1 right away and only need them to have access to the prep material on the site, you can simply add them to the 12 Day Detox Program level.
The system is pretty flexible for getting someone started in the programs.