what's the difference between cfm and static pressure.
CFM is cubic feet a minute. It's essentially how much air is shifted by a fan.
Static pressure (SP) is how forceful the fan is in a way. If something is blocking a fan which has high CFM but low SP e.g. an intake fan being blocked by a HDD, then the volume of air entering the system will be dramatically reduced.
Fans with high CFM but low SP are ideal for exhaust fans but must not be used on a cooler or radiator. if your case has good, unblocked intake fans, they can be used there as well.
Companies like Xigmatek offer fans that have very high CFM at reasonable volumes, but poor SP, whereas Noctura and Corsair do more expensive fans that offer both high CFM and high SP.