Program.cs
 

using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      string firstName = "John";
      string lastName = "Doe";
      string name = $"My full name is: {firstName} {lastName}";
      Console.WriteLine(name);
    }
  }
}

Result:
My full name is: John Doe