You can find the VLAN Settings at Interfaces → Assign → VLAN.
VT AIR currently supports 802.1q VLANs.
VLANs can only be configured on top of:
Bridges are an exception, their VLANs are configured in the Bridge settings. A VLAN on top of a Bridge is only useful if you want to have an IP in that particular VLAN. VLANs defined in Bridges are still routed in L2 on the Bridge and forwarded on the defined Bridge Ports.
VLAN ID can be set on the interface that you select for the VLAN.
Assign to new Interface is an option shown when you create a new VLAN and it will automatically assign the Interfaces as described in Assign Interfaces.
We have a Video Tutorial regarding the VLAN configuration: