First you need to prime the wall with a good fast drying acrylic primer. This will seal the wall and show all of the defects. Allow the acrylic primer a couple of hours of dry time then fix any defects.
Regular drywall mud can be used for the repairs, available in 1 gallon or 5 gallon containers or boxes. If time is a concern, consider purchasing a bag of setting mud. Setting mud is a powder that is available in various drying times, from 20 minute to several hours. (Check out <a href="https://www.house-painting-info.com/joint-compound.html">Drywall Joint Compound</a> for more details.)
Spot prime any dry drywall mud with the same acrylic primer after all repairs are finished. Then paint as usual.