In Illustrator, you can design patterns, complex graphics and work with type. You can learn to design printables fast with the Basic Printable Design Course from Printable Crush. Illustrator is a highly in-depth program, so taking a course is a quick way to learn the basics.
However, if you want to create something custom to fit your needs, you can learn to create your own! You'll need to choose the right software and learning program, and you'll be well on your way to making amazing and unique printables.