Slack notifications allow you to send notifications of deployments directly into a Slack room. For more information about Slack, visit their website.
To set up a new notification, click the Notifications link on the left hand side of your project, then the New Notification button to get started.
Enter your account name (your Slack domain) and the token (the last part of the webhook url) you've just generated, any customisation to the message format using variables found via the these variables link on the page, then finally the (default) option to display the message as rich text.
Choose when to send notifications, and choose any servers you wish to send notifications for, or keep the Send notification when any server or group deployed? option checked if you want to notify on all servers.
Finally, click Create Notification to finish.