You need to create VLAN IDs via that screen that match the VLAN IDs you're creating in pfSense. Then on Port 26, make sure each one of those VLANs is set to tagged. Voila, trunked port.
Then on your switch, if you aren't using VLAN sensitive gear, you need to go to each VLAN ID via the drop-down, set the ports you want on that network to Untagged. Then, go to the PVID list, and set the PVID for those ports to that same VLAN ID.
The Netgear does sort of have the options that shdesigns
is referring to, but it does it on a VLAN by VLAN basis. If you have a port set as Untagged for one VLAN, and 'Not Member' for every other VLAN, it will only pay attention to untagged traffic, and ignore any VLAN tags coming into it. Similarly, it will not send any VLAN tags.
If you have a port that is Untagged for one network (with matching PVID), and set another VLAN to be tagged, it will send both the tagged and untagged packets, as well as accept both. This would be useful if you have a VOIP phone with a computer on the passthrough port. The VOIP could be on its separate VLAN, while the computer is on its own network.