Fordyce granules are simply misplaced sebaceous glands located on movable oral mucosa. The sebaceous glands are supposed to occur in the skin and there they produce the oil that keeps our otherwise dry skin lubricated and supple. In the oral cavity, they serve no purpose, and in general, nature leaves them out of the oral tissues. But in some people, they occur in the oral mucosa where they do no damage, even though they are unnecessary. Most of the time you will see them on the inside of the cheeks as in the image above.
The image above shows them as small yellowish granular nodules covering the cheek mucosa, however, they can occur in other unattached oral tissues such as the unattached gingiva or under the tongue. They can occur separately as well as in masses as shown here.