'Cooling paste' is applied to your processor/ heat sink. It is there to conduct heat affectively so your system doesnt over heat and die. There are different types of paste, most poeple would say arctic silver 5 is the best to use. You have to have thermal paste applied or your hardware will over heat and damage itself. You shouldn't have to apply it often at all. But i would probably re apply it every so often (say 10 months or a year )