The files that IFS Construction Kit uses to save the iterated function codes or chaos game moves have extension .ifs and .chg, respectively. If these extensions are registered with Windows, then double clicking a file with extension .ifs or .chg should open that file in IFS Construction Kit. Since the program makes no changes to your Windows directory or to the Windows's registry file, you will need to register the file extensions yourself.
Click on a file with extension .ifs with the right mouse button and select open. Click on "Select the program from a list" and click Ok. In the resulting dialog box, click on the "Browse..." button and select your copy of the IFS Construction Kit program. Click Open. Make sure the box is checked for "Always use the selected program to open this kind of file". Now click Ok.Repeat this step by clicking on a file with extension .chg.
All your .ifs and .chg files should now show the icon for IFS Construction Kit (a small red Sierpinski triangle). Double click a file and it should open in IFS Construction Kit in the appropriate IFS mode or Chaos Game mode.
It is possible that another fractal drawing program you have installed on your computer has already registered the .ifs file extension for that program. In that case you will need to decide which program you want to use as the default to open an ifs file when you double click on it.
In versions of Windows before Vista, if you open "My Computer" or "Windows Explorer", the file types are listed under the menu "Tools/Folder Options..." (click on the "File Types" tab). Scroll down to the IFS or CHG extension and click on the Advanced button. Click on "open" and then the "Edit..." button. You will the "application used to perform the action". If everything is working properly, you should not need to change anything in this dialog box.
You may on occassions want to edit an ifs or chg file rather than open it in IFS Construction Kit. To make this easy to do, in the dialog box "Edit File Type", click on the "New..." button. For the Action, type "edit". For Application used to perform acton, use the "Browse..." button to find a program you use for editing text files (e.g. Notepad or Wordpad). Click Ok. Now when you right click on an .ifs or .chg file you should be able to select either "edit" or "open".
Unfortunately, the Folder Options window in Vista is missing the File Types tab as described above. You may be able to download a third-party program to edit file type associations in Vista.