Paging Frame (PF): One Paging Frame (PF) is one Radio Frame in which the UE is looking for paging message. One Paging Frame may contain one or multiple Paging Occasion(s).
Paging Occasion (PO): It is a subframe where there may be P-RNTI transmitted on PDCCH addressing the paging message for the UE. There is always only one paging occasion for each UE in a DRX cycle.
To find out PF (Paging Frame) and PO (Paging Occasion), the UE uses DRX parameters broadcasted in the system information SIB2.
For calculation of paging frame and paging occasion please follow below link. In this link they explain very well. Please go through RRC_IDLE: Part 1 and Part 2.