Quilling paper can be cut yourself with a ruler and a craft knife, made with a plotter, or purchased pre-cut.
But even here, the choices begin: How wide should the strips be? How long? And how thick should the paper be?
These decisions depend on what you want to create. For beginners, wider strips of about 1 cm are often easier to work with. The smaller the strips, the more challenging the work becomes. The length of the strips also depends on the shape you want to quill. Sometimes a short strip of a few centimeters is enough, while other times you need to glue several strips together to achieve the required length.
These are all pieces of experience you gather over time as you discover what works well and what doesn’t.