Hi R, you can import one of several Email Modules from the MarketPlace (like EmailTemplate). This module will provide you with email functionality. You will need to connect the Administration snippet to a page in your app and configure the email settings to your email provider in the runtime.
You can create email templates in the runtime. In the designtime you can code when which emailtemplate should be sent to whom and with what variables.
On your save button you now need a microflow.
This microflow should first Save the object (obviously)
Then from the available associations, get the User to whom the email has to be sent.
Now integrate the EmailConnector Appstore module.
It has an option to configure a Template and also defines helper (_USE_ME) microflows and javaactions to trigger the microflow.
You need to figure out a way to call the EmailConnector Microflow which helps you send the email by passing the FROM Address and the need body of the email and other things.
I suggest you first figure out how to configure EmailConnector Marketplace Module and send a Test Email. Then check the EmailConnector Module _USE_ME folder to see what it offers.