Does it mean I can use royalty free sound and image files in my games I sell? If not what if the license states that I can use those free resources in commercial games?
Royalty free means that you don't have to pay a percentage (a royalty) for each use of the resource. How you may or may not use it is in the licence.
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But always read the license.. Usually any royalty free asset (sound, image or templates) allows only 1 use for comercial projects. And you need to buy it again for another project.