Under Advanced -> Setup -> Internet Setup

1. Does your Internet connection require a login? Yes
2. Internet Service Provider PPPoE
3. Login in format AAAAAAAAAAZZZZZZZZZZZ#MMMM@t-online.de (see below)
4. Password is your personal password
5. Connection mode Always On
6. Apply

The internet will not work yet, you need to set VLAN ID

Under Advanced -> Advanced Setup -> VLAN / Bridge Settings

1. Check Enable VLAN / Bridge group
2. Check By VLAN tag group
3. Check in the line which says Internet and click Edit
4. Set VLAN ID to 7 and Apply (Priority can stay 0)

After a few moments your router will be online.

Login format

A = 12-digit connection identifier (Anschlusskennung)
Z = access number (Zugangsnummer)
M = four-digit shared user (for the main user 0001) (Mitbenutzernummer)

should be there only if access number is shorter than 12 digits

All above numbers can be found in a letter you should receive from Telekom