Running multi-file go program

So I'm pretty new to go and I'm trying to follow this tutorial -

http://thenewstack.io/make-a-restful-json-api-go/

Right now, this is my file structure -

EdData/
    dataEntry/
       populateDb.go
    main.go
    handlers.go
    routes.go

When I run go run main.go, I get this error ./main.go:11: undefined: NewRouter

This is what my main.go looks like -

package main 

import (
	"net/http"
	"log"
)



func main() {
	router := NewRouter()

	log.Fatal(http.ListenAndServe(":8080", router))

}

func checkErr(err error) {
    if err != nil {
        panic(err)
    }
}

This is what my routes.go looks like

    package main

import (
	"net/http"
	"github.com/gorilla/mux"
)

type Route struct {
	Name string
	Method string
	Pattern string
	HandlerFunc http.HandlerFunc
}

type Routes[]Route

func NewRouter() *mux.Router {

	router := mux.NewRouter().StrictSlash(true)
	for _, route := range routes {
		router.
			Methods(route.Method).
			Path(route.Pattern).
			Name(route.Name).
			Handler(route.HandlerFunc)
	}
	return router
}

var routes = Routes{
	Route {
		"Index",
		"GET",
		"/",
		Index,
	},
}

and this is what my handlers.go looks like

package main

import (
	"fmt"
	"net/http"
)

func Index(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintln(w, "WELCOME!")
}

When I try and build routes.go, I get that Index is undefined, and when I try and build handlers.go, I get

# command-line-arguments
runtime.main: undefined: main.main

How do I get this to run? Also, where do I execute the go run command? Do I need to manually build all the dependent files?

From the go run help:

usage: run [build flags] [-exec xprog] gofiles... [arguments...]

Run compiles and runs the main package comprising the named Go source files.
A Go source file is defined to be a file ending in a literal ".go" suffix.

Only the files passed to go run will be included in the compilation (excluding imported packages). Therefore, you should specify all of your Go source files when using go run:

go run *.go
# or
go run main.go handlers.go routes.go