Summarize the following:
Press the "Input" or "Source" button on your TV's remote to select the HDMI port that you connected the Apple TV to. The Apple TV usually turns on automatically, so you should see the menu to select your language. If you don't see anything, double-check your connections and then press the center button on your Apple TV remote. Use the remote to select your interface language. Use the center button on the remote to make your selection. If you are connected to the network via Ethernet, Apple TV will automatically detect the network and connect. If you are connecting via Wi-Fi, a list of available wireless networks will be displayed. Select the network that you would like to connect to. Enter your password if the network is secured. It may take a few moments for Apple TV to perform its initial setup process. After the setup process is complete, you'll be asked if you want to opt-in to the usage data collection program for Apple. Your Apple TV will work best when it's updated to the latest version of the software. You can check for updates using the Settings menu.  Open the Settings app on the Apple TV Home screen. Open the "General" option and then select "Update Software". Your Apple TV will check for and install any available updates.

Summary:
Turn on your TV to the correct input. Select your language. Connect to your network. Wait for the Apple TV to activate. Check for updates.