Once a VLAN has been created either on your router or USG (you can find our guide on how to create a VLAN on your USG here UniFi - USG: VLAN setup), this can be implemented into your switch network.
To create a VLAN profile that can be tagged to specific ports on your switch, you will need to go to settings > networks > create new network. You will need to select VLAN only for the purpose of the network to create the profile.
From here, you can name the network and enter the VLAN ID number that had been set up for that network. Once this is saved, you can start to assign it to specific ports on your switch.
You will then need to navigate to the devices page > select the designated switch > go to Ports tab. After editing the designated port, you can assign it the newly created VLAN port profile from the Switch Port Profile drop-down.
Once the settings have been applied, the port will then only pass traffic tagged with the assigned VLAN.