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 admin motto "click-not-code").
The notification will appear in Salesforce mobile app and Lightning experience (desktop web browser), but you can determine if you want the notification to appear in Salesforce mobile app only or the Lightning experience only, or both environments.
Only a few step an admin need to build notification.
1. Create Custom Notifications
This is where we determine where the notification will show, mobile or desktop, or both.
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"