because a struct is also a data type, it can be used as an anonymous field, the outer struct can directly access the fields of the embedded struct even if the struct came from a diffrent package. this behaviour provides a way to derive some or all of your implementation from another type or a set of types.
package main
type Admin struct {
    Username, Password string
}
type User struct {
    ID uint64
    FullName, Email string
    Admin // embedded struct
}
func main() {
    admin := Admin{
        "zola",
        "supersecretpassword",
    }
    user := User{
        1,
        "Zelalem Mekonen",
        "[email protected]",
        admin,
    }
    fmt.Println(admin) // {zola supersecretpassword}
    fmt.Println(user) // {1 Zelalem Mekonen [email protected] {zola supersecretpassword}}
    fmt.Println(user.Username) // zola
    fmt.Println(user.Password) // supersecretpassword
}