Ensure you are logged in. If you are not you can do so here
Go to settings and connect your twitch account, or click here to connect your twitch account
HDT users install the plugin. Firestone users don't have to do anything, unless they've previously disabled the integration in General -> Third Party (then reenable it 4head)
And that's it! Just stream hearthstone on twitch with either Firestone running or HDT with the plugin. After you finish a game it will be logged in Streamer Decks
NOTE: Streaming now functionality is currently unsupported. Streamer decks gets updated after you finish a game.