You can sell printables on Etsy, or on any other marketplaces like ebay, Zazzle, amazon, etc. . You do not need a sophisticated program to create digital printables, you can try creating templates on canva, it is free and easy to use. If you know photoshop and illustrator, that's fine but even if you do not know how to use these programs, you can still use a free tool like Canva to create printables. Another great program to create printables is adobe spark. Since this is the program created by the same people who created photoshop, I really like this adobe spark.