This is, of course, a small snippet of the possible cases you might need.  We're interested in a small visual control, so TGraphicControl is the best base class for us.  There's no need for TCustomControl because our component won't need window focus.

We can get started now.  Go to File->New and select component.  You'll be presented with a dialogue box.  Fill it out like this:

The only two things you need to fill out are the "Ancestor type" and "Class name" boxes.  The rest get filled out automatically.  Once you've done that,  click the OK button and you get transported to the code editor with a skeleton class written out.

First we need to let the compiler know what we'll be using.  Each unit (a file, usually containing a class) has a "uses" clause.  This lists what other files will be needed to compile the unit.  Without this the compiler would have a really hard job so it's up to us to make sure it's correct.

Note:
The following section about adding Graphics to the uses clause is relevant for Delphi 6 (and possibly Delphi 5).  Delphi 4 adds Graphics automatically so if you start a new component and the uses clause has "graphics" in it then you don't need to do the next part.

You usually don't notice the "uses" clause as it's filled out with a large number of units by default (such as classes, sysutils, etc.).  These units include most of the functionality you require.  However, sometimes you have to add your own units (which usually listed in the help files for the appropriate class/procedure/function/type).  We'll be needing the type TColor, which represents a colour.  If you look this up in the help file you'll see it's within the 'Graphics' unit.  Let's add that now before we start.  Go to the very top of the file and find the uses part.  It will look like this:

// <-- name of file without .pas
unit Line;  

interface

uses
  Windows, Messages, SysUtils, Classes, Controls

You can see that each unit needed is simply separated by a comma. We'll add Graphics to the uses unit. Make this change:

uses
  Windows, Messages, SysUtils, 
  Classes, Controls, Graphics; //(note added unit)

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