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.