Graphical Installer is an extension for NSIS. It allows to change the design of whole NSIS installer and it is also possible to create installers with irregular windows (Part of window can be fully transparent). This is a fourth generation of this extension and it has a lot of new features and improvements.

To create a NSIS installer, you first have to write a NSIS script. A NSIS script is just a regular text file with a special syntax. You can edit scripts with every text editor. It's recommended you use a text editor that shows line numbers because NSIS uses line numbers to indicate where errors lie, and to warn you about where errors might lie. An editor that supports syntax highlighting is also recommended.
For more details about the script format, see NSIS Script File Format.

The default extension for a script file is .nsi. Header files have the .nsh extension. Header files can help you arrange your script by dividing it to more than one block of code, you can also put functions or macros in header files and include the header files in multiple installers. This makes updating easier and it also makes your scripts easier to read.
For other information about NSIS script files visit NSIS documentation.

Each Graphical Installer powered installer epitomizes more sophisticated system. It links several NSIS headers and uses a few plug-ins to create required visual effects.

Installer is saved in its own .nsi file called <project>.nsi file where project represents installer's filename. This is main installer's file - this file is compiled into resulting .exe. This file contains link to all necessary files and this file is a heart of your future installer.
Graphical Installer powered installers are unique in fact that they need aditional file called <project>.graphics.nsh where resources for proper function of installer are defined.

With this two files you are able to create skinnable installers with all functionality as classic NSIS installers.
Please read <project>.nsi description and <project>.graphics.nsh description for more information.