如何从不同的文件中引用c#类?

我是编程新手，我正在尝试使用BBEdit的"TextWrangler"程序(类似notepad++，但适用于Mac)的Mono编译器学习c#。然而，我的问题非常简单:我试图在c#中编写一个非常简单的程序，该程序使用来自不同.cs文件的类。

我正在为此挣扎。如果类在同一个。cs文件中，我没有问题;否则，bash终端会一直给我错误。下面是我的代码:

Program.cs:

//  Client class, where Main method calls the Car method
using System;
using Auto;
namespace Auto
{    
    class Program
    {        
        public static void Main(string[] args)
        {        
            //Instantiate car class
            Car car = new Car("Toyota", "Corolla", "Sedan", 2014, 25000);
            Console.WriteLine(car.Maintenance());
            Console.Read();
        }
    }
}

Car.cs:

//  "Car" class (does NOT include the Main method)
using System;
namespace Auto
{
    public class Car
    {
        //Create various attributes for Car Class with getters and setters
        public string Make { get; set; }
        public int Year { get; set; }
        public string Model { get; set; }
        public string Type { get; set; }
        public int Millage { get; set; }
        public DateTime PurchaseDate { get; set; }
        //Constructor to instantiate Car object that pass all the necessary attribute values 
        public Car(string make, string model, string _type, int year, int millage)
        {
            Make = make;
            Model = model;
            Type = _type;
            Millage = millage;
        }
        //Maintenance method will check all the inspection that the mechanic has to do     based on the millage of the car
        public string Maintenance()
        {
            int index = 1;
            string maintenanceList = string.Empty;
            if (Millage > 5000)
                maintenanceList += (index++).ToString() + ". Oil Change " +Environment.NewLine;     
            if (Millage > 10000)
            {
                maintenanceList += (index++).ToString() + ". Check Brakes " +     Environment.NewLine;
                maintenanceList += (index++).ToString() + ". Rotate Tires " + Environment.NewLine;
                maintenanceList += (index++).ToString() + ". Lube Hinges, Lock, and Latches" + Environment.NewLine;
            }
            if (Millage > 15000)
                maintenanceList += (index++).ToString() + ". Replace air Cleaner element" + Environment.NewLine;
            if (Millage > 30000)
                maintenanceList += (index++).ToString() + ". Replace Dust and Pollen Filter" + Environment.NewLine;
            return maintenanceList;
        }
    }
}

就是这样。代码比看起来简单-但是每当我尝试编译这些文件时，这两个文件都保存在我的Finder中的同一文件夹下，我得到这些结果:

Program.cs:

Compilation failed: 1 error(s), 0 warnings
Program.cs(14,13): error CS0246: The type or namespace name `Car' could not be found.      Are you missing an assembly reference?
Program.cs(15,31): error CS0841: A local variable `car' cannot be used before it is declared

Car.cs:

error CS5001: Program `Car.exe' does not contain a static `Main' method suitable for an entry point

所以是的，我被困住了。我已经阅读了很多关于c#入门类构建的资料，但是我的运气没有任何收获。