You will be without clothes from the waist up and you will lie face down. The FMM is practiced almost solely on the back most of the times, and I use unscented high quality massage vegetable oil that doesn’t leave stains.
You can keep your pants or skirt on, or take them off to feel more comfortable.
Often you will need to have the upper part of your buttocks exposed, to work on your glutes. Your legs will be covered.