I am new to this since I have been coloring japanese cartoon characters in Photoshop. Now I want an upgrade and during the coloring session, I am having a little trouble on how to make the scanned lineart (which is the "canvas") into a layer? Is there a method to convert it as a layer or is it the other way around or should I do something about converting the JPEG to a PNG?

Note: I scanned my sketch through a scanner. I don't use a tablet to draw through computer. I only color through computer.