Visit the Gimp's website at www.gimp.org. There are various stable versions of the application, as well as potentially less reliable development versions. The page provides links to other sites where you can download the version of The Gimp you want. Click ‘Gimp for Windows' at the bottom left.
Click ‘Automated installer', which will take you to Jernej Simoncic's website. Select ‘Stable version' from the menu on the left. In theory you'll need 200MB of hard disk space to install the application, but with certain options turned off you'll be able to get away with around 30MB.
Before downloading The Gimp, you need to download the GTK Runtime Environment. This helps with the setup process. Click on the Download link below GTK+ 2 Runtime Environment. A screen will appear telling you the download is taking place. If this doesn't work, there's also a direct link.
Save the file to your desktop. Then double-click the installer file on the desktop to launch the GTK+ 2 Runtime Environment setup wizard. Follow the steps to accept the licence, select an installation destination, choose a full, compact or custom install and review the settings, then click Next.
Next choose your preferred language for GTK+ Runtime Environment and complete the installation. Now repeat step 3 to download the setup file for The Gimp application. You'll find the download link for this on the same page as for the GTK+ 2 Runtime Environment, as in step 2.
Double-click The Gimp installer icon on your desktop. Follow the setup wizard as before. Accept the licence agreement, select an installation destination and choose which components to install, which file types will be associated with the software and whether a desktop icon and quick-launch icon will be created.