From what was explained to me the other day.... you apply the .jpg texture in the material room to whatever texture you want to apply it to. Then add your different nodes if you want any. Then save the settings using the + button. I don't think that converts anything, and I don't know if you always have to apply the .jpg texture and then the material stuff afterward or if after saving you just have to apply the texture from the material folder. I never got that far. I didn't quite understand it all to be honest with you.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi