NPM is very easy to use. You can use it to manage your project's dependencies and you create commands for tasks automation purposes, everything is created and managed into the package.json file. See bellow a list of the top npm commands:
npm init: displays a simple wizard to help you create and describe your new project;
npm install module_name: install a module;
npm install -g module_name: install a global module;
npm install module_name --save: install a module and add it into the package.json file, inside dependencies;
npm install module_name --save-dev: install a module and add it into the package.json file, inside devDependencies;
npm list: lists all the modules installed on the project;
npm list -g: lists all the global modules installed on the OS;
npm remove module_name: uninstall a module from the project;
npm remove -g module_name: uninstall a global module;
npm remove module_name --save: uninstall a module from the project and also remove it from the attribute dependencies;
npm remove module_name --save-dev: uninstall a module from the project and also remove it from the attribute devDependencies;
npm update module_name: updates the module version;
npm update -g module_name: updates the a global module version;
npm -v: displays the npm current version;
npm adduser username: creates an account to <npmjs.org>;
npm whoami: displays details of your public npm's profile (you must create an account using the previous command);
npm publish: publishes a module into <npmjs.org> (it's necessary to have an active account first);