The Apple Developer Program is for software developers working with iPad, iPhone, and Mac. For more information about enrolling in the Apple Developer Program, see What You Need To Enroll from the Apple Developer website.
Using Jamf Now may require that you get an Apple Developer Program account, depending on your desired functionality:
You do not need an Apple Developer Program account to deploy files that are already in the PKG format.
In order to convert files in to a PKG, you will need to create that new package with a packaging tool, such as Jamf Composer, and sign that new package with your Apple Developer Program account ID.