Hi khampol,
I have the same setup, a pfSense VM as my primary homelab router (well all home router really).
If you have the Windows VM installed then Proxmox will have created the default linux Bridge vmbr0, that forms the LAN network/subnet.
The bridge vmbr0 should already have the subnet/mask and gateway completed (from Proxmox installation).
The other important section is the bridge ports: which points to the network interface card. The LAN side of pfSense will connect to vmbr0 on installation you can assign a different IP address (within the same subnet) e.g. I have Proxmox on 192.168.X.1/24 and pfsense on 192.168.X.254 - which becomes the network 'Default Gateway'.
For the WAN side you should create the 2nd bridge vmbr1, from your 2nd network adaptor, here only the Bridge port: info needs to be entered as you will set the mode (DHCP, PPPoE, Static IP, etc) after pfSense installation.
Both bridges should be attached to the VM before pfs installation.
Hope that helps
DerekG