The Wireless tab under Interfaces > (assign) is for creating and managing additional Virtual Access Point (VAP) interfaces. Using VAPs allows multiple networks with unique wireless SSIDs to be run off a single card, if that feature is supported by the hardware and driver in use. A VAP is created on the Wireless tab, then assigned on the Interface assignments tab. In-depth information on this feature can be found in Wireless.
VLAN tagged interfaces, or 802.1Q tagged interfaces, are located on the VLANs tab under Interfaces > (assign). VLAN instances allow the system to address traffic tagged by an 802.1Q capable switch separately as if each tag were its own distinct interface. A VLAN is created on this tab, then assigned on the Interface assignments tab. In-depth information on this feature can be found in Virtual LANs (VLANs).
The QinQs tab under Interfaces > (assign) allows creating an 802.1ad compatible interface that is also known as Stacked VLANs. This feature allows multiple VLAN tags to be contained in a single packet. This can aid in carrying VLAN-tagged traffic for other networks across an intermediate network using a different or overlapping tag. In-depth information on this feature can be found in pfSense QinQ Configuration.
Interface Bridges, or multiple interfaces tied together into a common shared layer 2 broadcast domain, are created and managed on the Bridges tab under Interfaces > (assign). More information on bridging, including how to create and manage bridges, is in Bridging.
After An OpenVPN instance is created, it may be assigned under Interfaces > (assign). Assigning an OpenVPN interface enables interface-specific rules, and allows the interface to be used elsewhere in the GUI that requires an assigned interface. This also triggers the creation of a dynamic gateway. This gateway can be used for policy routing, or in a gateway group for Multi-WAN. See Assigning OpenVPN Interfaces for more information.