I have attached a pic of the Apple-supplied two-wire cord.
The picture did not come through, but it sounds as if you are describing the AC power cord for the Time Capsule. This is not an Ethernet cable, as you mentioned above. Please confirm on that.
I assume the Time Capsule connects to the DSL Broadband, but I only have a two-wire cord. Have no idea how to proceed, and I am tech literate. Appreciate any help. Don't get on forums often. Usually solve my own problems. This one has me stumped.
Please spend a few minutes by reading through the Setup Guide that came with the Time Capsule.
In terms of hookup, you will need an additional Ethernet cable that will connect from one of the three yellow Ethernet ports on the ATT router to the WAN "O" port on the Time Capsule.
Then, follow the instructions in the Setup Guide to configure the Time Capsule.
This Apple Support document may provide additional details.
Setting up Time Capsule for the first time - Apple Support
You have 90 days of free phone support from Apple. If you need further assistance, give Apple Support a call and they will be able to walk you through the setup.