Every Go source file begins with a package clause. It is the first line of real code in the file, and it names the package that the file belongs to:
package main
A package is just a folder of Go files that share the same package name. All the files in one folder must declare the same package. The package is Go's unit of code organisation - the way you group related types and functions together.
The shape to remember: one folder is one package, and every file in that
folder opens with the same package name line.