Salesforce offers an easy way to notify a user, such as a record owner, team members, etc. You do not need to wring a single line of code to build this (if you prefer); remember the admin motto "click-not-code").
The notification will appear in the Salesforce mobile app and Lightning experience (desktop web browser), but you can determine if you want the notification to appear in the Salesforce mobile app only, the Lightning experience only, or both.
Only a few steps for an admin to build the notification.
1. Create Custom Notifications
This is where we determine where the notification will show: mobile, desktop, or both. Navigate to the Setup menu and search for Salesforce Notifications.
From the Setup menu, search for Custom Notifications; you can create or edit existing notifications.
Once added, the new custom notification will be added and shown under Notification Delivery Settings.
2. Send Custom Notification from Process Builder
In addition to using Process Builder, the notification also can be sent from Flow Builder, Apex, and API.
In the Process Builder, from Action Type, select "Send Custom Notification".