Most npm packages provide great documentation, followed by examples and use cases. As @sandeep said, npmjs is the official npm registry and is the de facto place to look for these resources. Also, large amount of the npm packages can be found at Github. npmjs provides a direct link to the repository if the package is on Github. If so, you should check the issues section, where people share their problems and ideas about the package. This will give you a general feel of how other people use the package.