There are several ways to share content in and out of CustomShow.
If you are planning to share a presentation from CustomShow to someone who does not have CustomShow, you will need to create and share a SlideShow.
Please see the article on Sending SlideShows.
If you are planning to share a presentation to another user in the CustomShow app, then you can simply change the level of permissions granted to that user.
To set permissions on a presentation, make sure that the presentation is open. In the Library Console, right-click on the presentation and choose Share...
For more information on Sharing Presentations, please see the article on How to Share a Presentation. You can also find out more about the different sets of permissions available in Permissions & Rules.