f you do very much graphic design you need to work in both Adobe Photoshop and Adobe Illustrator. They both have features the other program does not have. Photoshop is a wonderful painting program, but it is not a good drawing program. Photoshop files are raster, or pixel-based images. If you enlarge them, they will lose quality. Illustrator is a great drawing program and has many drawing tools Photoshop does not have. It also has very powerful tools for tracing images. Illustrator files are vector-based, or created using complicated algorithms. All you need to know about that is that you can scale them to any size without any loss of quality.
A good workflow would be to finish a drawing, scan it, and open it in Illustrator. You can trace the image with Illustrator and save it as an .ai file. If you are really good with the Pen tool, you can select each line in the image and make it look perfect. If you want to color the image in Photoshop, just find the file on the drive where you saved it, right-click on it and select Open With > Adobe Photoshop. After you color it in Photoshop you can save it as a .psd, or .jpeg, or .png file.