To work effectively with modules in Node.js, you need to understand how Node.js finds and loads them. This process is called module resolution. When you use the require function to import a module, Node.js follows a specific algorithm to locate the file or package you are requesting. The resolution process takes into account file extensions, folder structure, and even the presence of special files like package.json.

Node.js first checks if the module you are requiring is a core module, such as fs or http. If it is not a core module, Node.js treats the string you pass to require as either a relative path (starting with ./ or ../), an absolute path, or a module name. For relative and absolute paths, Node.js tries to resolve the file by checking the following in order:

• If the exact file exists with the given name;
• If the file exists with a .js extension added;
• If the file exists with a .json extension added;
• If the file exists with a .node extension added.

If the path points to a directory, Node.js will look for a package.json file inside that directory. If it finds one, it will use the main field to determine which file to load. If there is no package.json or no main field, Node.js will look for an index.js, index.json, or index.node file inside the directory.

If you require a module by name (not a path), Node.js will search for it in the node_modules folders, starting from the current directory and then moving up the directory tree until it reaches the root.