what is npm global install

npm install npm@latest -g

flag for npm install ... installs a module globally on your system.
good for tools, utilities you will use in more than one project
--global flag when running the install command
it puts the module in a system directory
rather than locally (to the current directory).

npm install package-name -g

npm install package-name

To save as a dependency:
npm install package-name --save