Often before a customer is ready to purchase a collection of videos it is super handy for them to be able to preview your content, this is where you might want to make an introduction video in the collection that is free. This differs from a trailer as it gives you a chance to show the quality of your content in a meaningful way.
Navigate to the collection you want to set a video as free under Content > Collections and click Edit. Under the Playlist tab you can toggle Available for free.
On the collection page, the free video will appear without the lock icon and anyone will be able to play the video without logging in or purchasing the collection.