下雪程序

我这有个桌面下雪的程序，但一直看不懂，麻烦各位帮我解答解答这里每个函数有什么用？
这个是win32的程序，这个感觉很难，不懂

using System;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Text;

namespace Snow
{
public class Win32
{
#region Win API functions

        public delegate void TimerProc(IntPtr hwnd, uint uMsg, uint idEvent, uint dwTime);//产生时间

        [DllImport("user32.dll")]
    public static extern uint SetTimer(IntPtr hwnd, uint nIDEvent, uint uElapse, TimerProc lpTimerFunc);//设置时间

        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);//查找窗口，是否越界

        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);

        [DllImport("user32.dll")]
        public extern static System.IntPtr GetDC(System.IntPtr hwnd);

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool RedrawWindow(IntPtr hWnd, ref RECT lprcUpdate, IntPtr hrgnUpdate, RedrawWindowFlags flags);

        [DllImport("user32")]
        public static extern int ReleaseDC(IntPtr hwnd, IntPtr hDC);

        [DllImport("gdi32.dll")]
        public static extern int SaveDC(IntPtr hdc);

        [DllImport("gdi32.dll")]
        public static extern IntPtr CreatePen(int fnPenStyle, int nWidth, int crColor);

        [DllImport("gdi32.dll")]
        public static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);

        [DllImport("gdi32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool LineTo(IntPtr hdc, int nXEnd, int nYEnd);

        [DllImport("gdi32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool MoveToEx(IntPtr hdc, int X, int Y, IntPtr lpPoint);

        [DllImport("gdi32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool RestoreDC(IntPtr hdc, int nSavedDC);

        [DllImport("gdi32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool DeleteObject(IntPtr hObject);

#endregion

#region Win API constants

        public const int WM_TIMER = 0x0113;
        public const int PS_SOLID = 0;

#endregion

#region Structs

        [StructLayout(LayoutKind.Sequential)]
        public struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
            public RECT(int left, int top, int right, int bottom)
            {
                this.left = left;
                this.top = top;
                this.right = right;
                this.bottom = bottom;
            }
        }

        #region Win API enums

        public enum RedrawWindowFlags
        {
            RDW_INVALIDATE = 0x0001,
            RDW_NOERASE = 0x0020,
            RDW_ERASE = 0x0004,
            RDW_UPDATENOW = 0x0100
        }

        #endregion

        #endregion
    }
}

另外这有全部的代码 --------------------编程问答-------------------- 这里只是对api的声明，根本不涉及任何实质性的代码 --------------------编程问答-------------------- 那这段代码是需要自己写的吗？
（我是初学C#的） --------------------编程问答-------------------- 你的目的是什么？？
想修改? --------------------编程问答-------------------- 说不是一两句能说清的，这些都是常见的 API 函数，搜索每个函数名，有大量的文章帖子解释这些 --------------------编程问答-------------------- 典型的API函数，这些东西都是规定死的，知道怎么用就行啊，没必要去深追究啊！！！ --------------------编程问答-------------------- API声明而已，不需要写，用pinvoke工具就能导入，个别没有的再自己转 --------------------编程问答-------------------- lz想问什么
这些只是封装好了的api函数
去百度一下 --------------------编程问答-------------------- 这些只是API函数，不用研究为什么知道是什么功能需要的时候拿来用就好了！

补充：.NET技术 ,  C#