You can learn to design printables with free options like Canva, or Paint. These programs are fine for basic designs, but can be very limiting. If you would like completely custom designs, programs like Adobe Photoshop and Illustrator are excellent.
The great thing about printables for personal use is that you don't need to have a fancy printer or pay a printing company a fortune. Simply print graphics at home with an inkjet or color laser printer. You can find a printer for as little as $60 or upwards of $2000. Don't think you need an expensive printer to create incredible graphics. A printer in the $100 range should work fine.