How do I write php code to send JSON data from MySQL database to my AngularJS application

How do I write php code to send JSON data from MySQL database to my
AngularJS application

I'm trying to wire up my angularjs application to get JSON data from a
database (mySQL), using PHP as the server-side language (a language I
taught myself this summer, and am most comfortable with).
Having looked at these links: (Angular JS: Full example of
GET/POST/DELETE/PUT client for a REST/CRUD backend?) (How to access the
services from RESTful API in my angularjs page), I feel very confident in
how the AngularJS code should look, but I don't know what the URL is doing
in these $resource examples.
I've never implemented a RESTful API in any language, and I'm having a lot
of trouble understanding what the code should be inside the tags.
Explanations on the web are often too technical for my skill level. I've
tried asking my professors, but I haven't found one who has implemented
REST before.
I appreciate any time and any help, Andrew