Sorry, WD, I'll try to be more specific in the future. Priming is nothing more than coating the bare plastic of your model with a sprayed on Compound called , well, Primer. It's a type of paint that offers a smooth, Homogeneous (all one kind) surface for the paint to adhere to. You can find it in most Auto body shops or Paint stores. I prefer light grey, as this also helps hghlight any errors I might have made in construction(glue spots, seams, etc.). The best way I've found to use it( Not THE best way, just MY best way...

) is this:
1. build up your model into major sub- assemblies( fuselage, tail, landing gear, etc. If you've got a cockpit, this should usually be assembled & painted prior to gluing it into th fuselage.
2. wash your model thoroughly with warm(not hot!) water and a little dish liquid. use a soft brush (old toothbrush works great) to get into all the panel lines.
3. rinse & dry well with a lint free cloth. I use cotton 'nappies(UNused, of course!) as they're absorbent & very soft- no scratches.
4. Mount the model on a painting frame- a wire hanger cut & inserted into any covenient opening will do.
5. Mask any areas you don't want painted: Cockpit, Clear lenses, Landing gear wells, whatever.(masking is coverin & taping with "masking" tape, just in case that's a new saying to you...)
6. Holding the model by your paint frame(you could also mount it to a desk or other surface- mine is on a plate which sits on a rotating base) Lightly mist on a coat of the primer from about 10"(25mm) away. Don't worry if it doesn't cover the whole model, you actually want that. After this coat dries, lightly mist another coat, paying more attention to the areas missed on your last coat. repeat only until the entire model is a uniform color.IMPORTANT safety note- Do this outside on a calm day. This primer is toxic in large amounts
7. set the primed parts aside to dry for 24-48 hrs. this will allow any volatile compounds in the primer to evaporate. Any flaws noticed in the finish of the model can be fixed & touched up after this 'drying out' period.
8. your model is ready to paint! Enjoy!