Step 1 : goto oneSignal.com and login into it. click here
Step 2 : A code will be generated after login, Copy and paste that code into Notification Details given in the website settings of your Admin Pane.
Step 3 : Your visitors will have to subscribe your site by a Bell Icon given in the right corner in the bottm and click on Allow Notification.
Now you are ready to notify your subscribers.
Tags : Browser Notification, Notification Details, Allow Notification