Questions about Blenders Texture Painting. Texture painting is a tool used to paint textures on to an object in real time. (both in the 3D view, and the UV Image Editor)
Blender features a built-in paint mode called Texture Paint which is designed specifically to help you edit your UV textures and images quickly and easily in either the Image Editor or the 3D Viewport. Since a UV texture is just a special-purpose image, you can also use any external paint program, like GIMP, Photoshop, or Krita.
Since a mesh can have layers of UV textures, there may be many images that color the mesh. However, each UV texture only has one image.
Texture Paint works in both a 3D Viewport and the Image Editor. In the 3D Viewport in Texture Paint Mode, you paint directly on the mesh by projecting onto the UVs.
See more information at the Blender Manual