To set up an ADSL connection on the Draytek 2862ac you will need to access the router interface through a web browser. To do this make sure you're on a device that is connected to the router, open a web browser, and then type the IP address of the router (192.168.1.1 by default) into the address bar then press enter. You will then be asked to log into the router.
By default, the username and password are both admin, but the password should have been changed if you've previously set up the router and haven't reverted to factory settings.
Once logged into the router you need to navigate to WAN > Internet Access on the left-hand menu.
Once on the Internet Access page click Details Page on the WAN1 interface.
The settings should be left as default other than entering the Username and Password in the ISP Access Setup section, which will have been emailed to you and you can also. Once completed the settings should be as follows:
If the settings are correct then click OK at the bottom and the router will connect.