To activate Disney Plus on Chromecast, follow these steps. First, connect your Chromecast to your TV and ensure it's linked to the same Wi-Fi network as your mobile device or computer. Open the Disney Plus app or go to disneyplus.com login/begin on your browser. Log in to your account and select the content you wish to watch. Tap the "Cast" icon at the top right corner of the app, then select your Chromecast device. Your content will start playing on your TV, and you can control playback from your mobile device or computer. Enjoy streaming Disney Plus effortlessly!