Discord announcement channels are special channels that have a megaphone icon instead of a hashtag. Users can follow these channels and automatically post them outside of the server every time you publish an announcement. This makes them a powerful tool for updating your community, even if they don't regularly visit or talk.
To create an announcement channel, you will first need to to login to Discord and navigate to your community server, after that click the plus icon next to the category you want to create the channel in. A menu should appear with the types of channels you can create, click the Announcement option and then type the channel name in the form.
The grey box you can see is an embed field, these are usually only enabled by bots. You can search Discord Bots to find a bot that can do this.
You can enable this in server settings under the overview page by toggling "send a random welcome message when someone joins this server"
You will need to find a bot that enables live stream notifications, one popular one you could use is MEE6