Web Push Notification: How to use Web Push PHP Library?

Take a look at https://web-push-book.gauntface.com/ for a general introduction to Web Push. The Chapter How Push Works and Subscribing a User should be particularly interesting to you. In summary:

• At the client side you need to create a subscription by calling pushManager.subscribe. More info here.
• You should send this subscription to your server. For example, make an AJAX request to send the subscription (endpoint, keys.p256dh, keys.auth) to the server. More info here.
• On the server you send a push message using the PHP Web Push library. First, you need to configure this library with your keypair. Then, you need to use the subscription (endpoint, keys.p256dh, keys.auth) to send a push message. More info here.