Summary: If you have Visual Studio 2005, here are some tips to get started.
Nearby: FrequentlyAskedQuestions

Download the appropriate version from the Spec# Website
Install Simplify from HP Labs as described here
Start Visual Studio 2005 and create a Spec# console application. It may provide a default Program.ssc file, which is a Spec# Source Code file.
Make the file Program.ssc look like this.

---

using System;

public class Program
{
static void Main()
{
string! message = "Spec# says hello!";
Console.WriteLine(message);
Console.Read();
}
}

---

Now, compile it and run it.