the program that you link to doesn't contain a main function (or more properly in GO terms, a package named main, that itself contains a function called main which is the entry point of the program (well before main there can also be a function called init that is used to initialize data. take a look at the flag package ))
The fastrand repository that you linked to is supposed to be run as a library from other go programs that are going to use the functions it exposes. For example to get an integer from 0 to n [0, n) using this library you can use this toy program.
package main
import (
"fmt"
"github.com/NebulousLabs/fastrand"
)
func main() {
//prints a random int [0,10) using fastrand
fmt.Printf("random int:%d
", fastrand.Intn(10))
}
put that in a directory under your GOPATH, (let's say you name it foo.go) run
go get github.com/NebulousLabs/fastrand;
go build foo.go;
./foo;