• Create Assembly/DLL which will contain components.
  • Add New Project to current Solution as Class Library. Go to File > New > Project, or in Solution Explorer:
    • Select Solution, right-click Add > New Project.
    • Select “Class Library” from Templates (Project Types: Visual C# > Windows > Class Library).
• Create a Component.
  • Add Component to current Class Library project. Go to Project > Add Component…, or in Solution Explorer:
    • Select class library, then right-click, Add > Component.
• Modify the Component code. Eg:

  using System;
  using System.Collections.Generic;
  using System.ComponentModel;
  using System.Diagnostics;
  using System.Text;
   
  namespace libCustomApp
  {
      public partial class AppCustomizationConfig : Component
      {
          //-----------------------------------------------------
          // Fields
          //-----------------------------------------------------
          private string m_About = "Customization component for applications";
          private string m_Company = "ACME, Inc.";
          private string m_Copyright = "Copyright © 2009, ACME";
          private string m_Website = "http://www.acme.com";
          private string m_Software = "Sample Software";
          private string m_Custom = "My Software";
          private string m_CCny = "001";
          private string m_Mutex = "CompanySoftwareMutex";
   
          //-----------------------------------------------------
          // Properties
          //-----------------------------------------------------
          public string About
          {
              get { return m_About; }
              set { m_About = value; }
          }
          public string Company
          {
              get { return m_Company; }
              set { m_Company = value; }
          }
   
          //-----------------------------------------------------
          // Methods
          //-----------------------------------------------------
          public AppCustomizationConfig()
          {
              InitializeComponent();
          }
   
          public AppCustomizationConfig(IContainer container)
          {
              container.Add(this);
   
              InitializeComponent();
          }
      }
  }

• Walkthrough: Authoring a Component with Visual C#
• Component Designer
• How To Load Assembly at Run-time, i.e. Late Binding

System.Object
  System.MarshalByRefObject
    System.ComponentModel.Component
      System.Windows.Forms.Control
        System.Windows.Forms.ScrollableControl
          System.Windows.Forms.ContainerControl
            System.Windows.Forms.UserControl

Source: Creating Custom .NET Controls in C#, http://www.ondotnet.com/pub/a/dotnet/2002/03/18/customcontrols.html?page=1, O'Reilly Windows Dev Center.