Hi Jennifer, Skim coating refers to the application of drywall mud, or joint compound, to the entire wall surface to fill in and cover defects in the wall surface. This will provide a fresh, new base for either painting or new wallpaper. Before applying the skim coat however, the wallpaper paste must be removed from the existing surface. Buy a bottle of "DIF" from a hardware store and apply using a spray bottle and hot water. It will dissolve the wallpaper paste and then can be wiped with a sponge to remove the residue. It is very important that all paste be completely removed or future application of paint will alligator and not bond properly. After the wall dries, apply joint compound to the entire wall using at least a 6 inch wide drywall knife and a finisher's "mud pan" to hold the compound while "skimming". The idea here is to put mud on the knife and "skim" the knife across the surface, effectively filling in dents and dings and removing any that does not need to be there. It is important to clean the knife off on the pan frequently to remove excess compound and keep it from smearing. After completing the skimming process the wall should be allowed to dry and then lightly sanded with 100 grit sandpaper, to remove any dried excess mud. Word to the wise: Do Not rely on sanding to correct a poor application of drywall compound. The material is much easier to deal with when wet, and reduces dust that will made. If you've never worked with drywall compound and you want a perfect job, I'd have a handyman do this for you. Good Luck.