Need a RestAPI example for my database

Looking for an RestAPI example:

- for interface for an external app into MySQL/PHP
- and output from MySQL to external app
- and an authentification example with the MySQL database (password encryption file needs to be included)

This all is just the preperation for an external App.
I Do have a Database based in MySQL but i Need an Interface by RestAPI as a preperation for an external App,

So i just Need an example how this will work Cause i cant do that on my own.

Dear wedesigners, Please help!