REST is an acronym for REpresentational State Transfer and an architectural style for distributed hypermedia systems. Roy Fielding first presented it in 2000 in his famous dissertation.
Like other architectural styles, REST has its guiding principles and constraints. These principles must be satisfied if a service interface needs to be referred to as RESTful.
Composer is a tool for dependency management in PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you.
composer require samy/restapi
Please see Composer for more information.