What I do is I add my beer to my keg and close it all up then hook up my CO2 lines to the keg. After that is done I turn up my pressure to 25 psi and purge as much of the atmospheric air from the keg as I can,(usually pull the pressure release valve quickly about 8-10 time), this keeps oxygen and other unwanted gases out of your beer. Then I leave the keg pressure set to 25 psi for 2 days. After 2 days your beer should be sufficiently carbonated and good to drink. Set your pressure to the serving pressure(about 8-12 psi) and enjoy.