A paygate is a method for designating part or all of a bundle as requiring payment to download.
What content exists in front or behind a paygate is really up to the artist and publisher. BitTorrent recommends putting enough content before the gate to entice people to purchase the entire bundle. This sample content can include a shortened track, a trailer, or the first chapter of your book. The Now team is happy to work with you and advise you on what they've seen work with other content producers.
Should you seek advice, please contact the Now Publisher Support Team.