HA and IP's

I have two physical devices that I'm trying to create a cluster. Following F5 documentation I use the setup wizard to create the HA cluster. One document speaks of 3 different IP addresses (configsync, Failover IP address and Mirroring). For the config sync address it says it uses the self ip addess for the internal vlan, ok fine. For the Failover IP address it says to use the self ip addresses you used for vlan HA or vlan internal, of fine. For the mirroring it says it will use either the vlan HA or the self IP of vlan internal, of fine. So, following the document to create an active\standby cluster it asks for a floating IP for the internal vlan- so I gave it one and it said to put that vlan on interface 1.2 untagged, ok. Did the same for the external vlan but wouldnt let me put the vlan on interface 1.2 as instructed by the documentation since the internal was already on it, makes sense, but just following the instructions. Then it asks for a HA self IP - what do I use as this? Is this a new IP I need? Or is this one of the (config sync, failover or mirroring IPs I can use)??? Thanks.

Sometimes the documentation misses the big picture in explaining things. I wish they could explain all this in a simple overview instead of many different documents where it becomes easy to get lost.