If you plan to paint over wallpaper instead of removing the wallpaper first then you need to prime the wallpaper first using a paint primer that is alkyd-based.
Make sure you use the alkyd-based primer because any other primer will not work for painting over wallpaper.
A good paint primer for painting over wallpaper is Benjamin Moore Fresh Start All Purpose Alkyd primer.
Then you can use any other type of paint that you want to paint the room with and you may need to give the wallpaper a few coats of paint to fully cover it up.
However I would recommend for the really best results to remove the old wallpaper and make sure all the glue and residue is off and then prime the wall and then paint it.
But painting over wallpaper can be done if you want to do so.