Friend bought his first computer. What router does he need for AT&T DSL?

[Dennis S]

He has never used a computer except a few times at school before he retired from teaching. I saw him in Walmart and steered him to a Dell laptop with i3, 6 GB RAM and a 500 GB HDD for $350. I have never used a router so I know nothing about how to help him get started. I assume he'll need to buy it from a site with a phone number.