A module is how Go groups a project’s packages under one path. To start one, run go mod init in the project directory. It creates a go.mod file that records the module path and later tracks dependencies in The Golang Official Documentation
I’ll show you how to use it while building oru first project.
You normally initialzie the module once, at the project root. You can still run a single file with go run main.go but when you want Go to run the package in the module directory, use go run .