- Get a YouTube API key - this is free, but by default is limited to 10k requests per day. Just don't go constantly refreshing the page and you should be fine. Place this key in the API_KEY variable. This page should help you here.
- Add your favorite channels to the CHANNEL_IDs variable. You can find a channel ID by going to the channel's page->About (click on the description)->Share->Copy channel ID.
- Load the page in a browser. It should work! If it's not working, try reading the console to decipher any possible errors.