• Create a directory:

  using System.IO;
  class DirectoryUtil {
      public static void Main() {
          Directory.CreateDirectory("C:\\projdir");
      }
  } 

• Create subdirectory:

  Directory.CreateDirectory("C:\\projdir\\subdir1");

• Move a subdirectory:

  Directory.Move("C:\\projdir\\subdir", "C:\\projdir2");

• Delete directory:

  Directory.Delete("C:\\projdir");

• Copy or Rename a file:

  File.Copy( "c:\\file1.jpg", "c:\\temp\\file2.jpg");

• Move a file:

  File.Move( "c:\\file1.jpg", "c:\\temp\\file1.jpg");

• Delete a file:

  File.Delete( "c:\\file1.jpg" );

• Check if directory exists:

  if (Directory.Exists(folderBrowserDialog1.SelectedPath))
  {
      // do something
  }

• See full list of available System.IO.Path methods: Path Members
• Get FileName or FilePath (See Path.GetFileName() Method or Path.GetFileNameWithoutExtension() Method):

  string fileName = @"C:\mydir\myfile.ext";
  string path = @"C:\mydir\";
  string result;
   
  result = Path.GetFileName(fileName);
  Console.WriteLine("GetFileName('{0}') returns '{1}'", 
      fileName, result);
   
  result = Path.GetFileName(path);
  Console.WriteLine("GetFileName('{0}') returns '{1}'", 
      path, result);
   
  // This code produces output similar to the following:
  //
  // GetFileName('C:\mydir\myfile.ext') returns 'myfile.ext'
  // GetFileName('C:\mydir\') returns ''

• Get file list:

  public void GetFileList(dirpath)
  {
    DirectoryInfo dir = new DirectoryInfo(dirpath);
    FileInfo[] dirfiles;
    string filemask = "*.jpg";
   
    if (filemask != "")
    {
        dirfiles = dir.GetFiles(filemask);
    }
    else
    {
        dirfiles = dir.GetFiles();
    }
   
    foreach(FileInfo f in dirfiles)
    {
        lstImgLibrary.Items.Add(f.Name);
    }
  }

• Get application startup path:

  public string GetAppPath()
  {
    return Application.StartupPath;
  }

• Get temporary path:

  string m_Filename = System.IO.Path.GetTempPath() + "\\" + filename;

• Read registry key:

  using Microsoft.Win32;
  ...
  RegistryKey hklm = Registry.LocalMachine;
  hklm=hklm.OpenSubKey("HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0");
  Object obp = hklm.GetValue("Identifier");
  Console.WriteLine("Processor Identifier :{0}",obp);

• Delete registry key:

  RegistryKey OurKey = Registry.Users; // Create OurKey set to HKEY_USERS 
  OurKey = OurKey.OpenSubKey(".DEFAULT", true ); // Set it to HKEY_USERS\.DEFUALT 
  OurKey.CreateSubKey("OurSubKey"); // Create the key HKEY_USERS\.DEAFULT\OurSubKey 
  OurKey.CreateSubKey(@"OurSubKey\Subkey"); // Create a sub key HKEY_USERS\.DEFAULT\OurSubKey\Subkey 
  OurKey.DeleteSubKey(@"OurSubKey\SubKey"); // Delete the subkey name "subkey" 
  OurKey.DeleteSubKeyTree("OurSubKey"); // Delete the whole subkey and any subkeys below it

• Other examples:

  private string GetNoahModulesPath()
  {
      // The name of the key must include a valid root.
      const string userRoot = "HKEY_LOCAL_MACHINE";
      const string subkey = @"\Software\HIMSA\NOAH\Version 3.0\Modules";
      const string keyName = userRoot + subkey;
   
      return (string)Registry.GetValue(keyName, "DefaultPath", @"C:\Program Files\HIMSA\Modules");
  }
   
  private string GetNoahVersion()
  {
      // The name of the key must include a valid root.
      const string userRoot = "HKEY_LOCAL_MACHINE";
      const string subkey   = @"\Software\HIMSA\NOAH\Version 3.0";
      const string keyName  = userRoot + subkey;
      string NhVersion      = "0";
   
      if (Registry.GetValue(keyName, "", "") != null)
      {
          NhVersion = "3.0";
      }
      else
      {
          NhVersion = "0";
      }
      return NhVersion;
  }

Source: William Blum, http://www.wblum.org/smallsamp/copyclient.html

private Bitmap MakeImageOfClient()
{
    Bitmap bm;
    using (Graphics g = CreateGraphics())
    {
        bm = new Bitmap(ClientSize.Width, ClientSize.Height, g);
        using (Graphics h = Graphics.FromImage(bm))
        {
            Point source = PointToScreen(Point.Empty);
            h.CopyFromScreen(source, Point.Empty, ClientSize);
        }
    }
    //bm.Save("C:\tmp\sample.bmp");
    return bm;
}