You can use an Ethernet cable, but the wires from the router to the TV and Apple TV can be troublesome. In this case, you may need to use Wi-Fi.
How to connect your Apple TV to Wi-Fi
1. Open the Settings app, which has an icon that looks like a gear.
2. Scroll down to and open “Network.”
3. Click on the box under “Connection.”
4. Your Apple TV will scan for nearby Wi-Fi networks. Once it appears, scroll down to and select your network in the list.
5. Enter your password on the authentication page.
6. When done, your network will be listed as the top network, separated from the list of the rest of the available networks. On the Network page, your Wi-Fi network will be listed in the box under “Connection.”