I’m sure you have visited a website and have seen a notification box (in chrome, firefox, safari) that says “show notifications from this website”
Install this plugin > https://wordpress.org/plugins/onesignal-free-web-push-notifications/
Activate the plugin
Go to onesignal.com and create an account
One logged into One Signal you should see a box that says “Create a New App”
Go to App Settings in the menu on the left and then click configure on the web push notification for Chrome / FireFox. Fill in the details for you domain and a default image if you have one.
One the Keys & ID’s tab, copy the OneSignal App ID and the REST API Key. Paste them into your plugin settings.
Configure some or all the settings you want on the same screen. Here is one change I made