Click on "+" button on the bottom right corner to add a new website limit.
Enter the website URL, action and the time limit you want to set for the given website. The default action will be blocking the further usage for the entered website, when the entered time limit is up. However, you can also pick any of the "Send Notification" or "Show Dismissible Popup" options if you want to be notified but not be blocked.
Have a look at our YouTube videos to see how these three actions work in practice: