If someone could help me and explain me how to make murals I would be very glad:D...I didn't knew where to put this so I put it in the help section

Um...ok...I know I'll look like a noob...but...PLZ tell me how to upload something I recolored...I mean...I imported it into the game...but I don't know what to do next (....how can i put it into a file and ... this stuff...I know there's a turorial out here but i coudn't find it ...thanks