Composer is an application-level package manager for the PHP programming language that provides a standard format for managing dependencies of PHP software and required libraries. It manages them on a per-project basis, installing them in a directory (e.g. vendor) inside your project.
An interface is a programming structure that allows the computer to enforce certain properties on an object. In object oriented programming, an interface generally defines the set of methods that an instance of a class that has that interface could respond to. It is actually a concept of abstraction and encapsulation.
NPM stands for Node Package Manager, which is an application and repository for developing and sharing JavaScript code. To publish and install packages to and from the public NPM registry or a private NPM registry, you must install Node.js and the NPM command line interface using either a Node version manager or a Node installer.
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 requires PHP 5.3.2+ to run. A few sensitive PHP settings and compile flags are also required, but when using the installer you will be warned about any incompatibilities.
