You can find the PPPoE Settings at Interfaces → Assign → PPPoE.
PPPoE can only be configured on top of:
PPPoE is commonly used for DSL dial in connections.
Username is the PPPoE Username.
Password is the PPPoE Password.
Master Only can be enabled or disabled. In case of a HA setup, this PPPoE is only added to the master device. It’s disabled by default.
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.
10.9.1. DSL Connection via PPPoE¶
We have a Video Tutorial regarding how to create a DSL connection via PPPoE: