To install Discovery Plus on FireStick, start by powering up your FireStick device and navigating to the home screen. Go to the search icon on the top left corner and type "Discovery Plus" using the on-screen keyboard. Select the Discovery Plus app from the search results and click on it. Choose the "Download" or "Get" option to install the app on your FireStick. Once installed, open the app and log in using your Discovery Plus account credentials. You can now explore a vast array of content including documentaries, series, and shows offered by Discovery Plus on your FireStick device.