In typical deployments, your F5 device will have interfaces on both an external VLAN and an internal VLAN. The Virtual Server IP Addresses usually reside on the external VLAN while the pool member/server addresses are usually on the internal VLAN. When a packet reaches a Virtual Server, it's destination address is that of the Virtual Server. The F5 device will then send the packet to the Pool Member/Server, translating the destination address at the same time.
External and Internal are simply terms used...they don't necessarily mean public facing/internal facing. Typically, just consider them "Virtual Server VLANs" and "Pool Member/Server VLANs." I hope that answers your questions.
Nimbostratus
