Article: Click Image → Canvas Size. In the window that appears, click the chain icon to unlink the width and the height. Change the canvas size to a size that shows the subject well, and ensure that both width and height are set to the same number.  Use the Offset values to center the image in your new canvas before clicking the Resize button. Once you've resized the image, right-click on the layer and select "Layer to Image Size". This will change the layer boundary to match the canvas size. If you want, you can use GIMP's color tools to change the coloration of the image. The easiest way to do this is to click Color → Colorize and then play with the settings until you find the color you feel looks best. The final step in creating an icon is ensuring that the image supports all the different icon sizes. This is essential if you want to be able to use the icon in different areas of the operating system and want them to scale when icon size is increased or decreased.  Copy the layer. Click the Layer in the Layers window and press Ctrl+C. Scale the original layer. Open the Scale tool by pressing ⇧ Shift+T and change the image scale to 256 X 256 px. Click Image → Fit Canvas to Layers. (Note: if you are creating the icon set for OS X, start with a 512 X 512) Create the first copy. Press Ctrl+V to paste the layer. Click Layer → To New Layer. Open the Scale tool and change the size to 128 X 128. Create the second copy. Press Ctrl+V to paste the layer. Click Layer → To New Layer. Open the Scale tool and change the size to 48 X 48. Create the third copy. Press Ctrl+V to paste the layer. Click Layer → To New Layer. Open the Scale tool and change the size to 32 X 32. Create the fourth copy. Press Ctrl+V to paste the layer. Click Layer → To New Layer. Open the Scale tool and change the size to 16 X 16. You should have 5 layers, each one with an image smaller than the last. If any of them look blurry, open the Sharpening Tool by clicking Filters → Enhance → Sharpen. Adjust the slider until the image is clearer. Click File → Export. In the Export Image window, change the extension in the top field to ".ico" and choose a location to save the icon. A window will appear, asking if you want to compress any of the layers. Check the box to compress the two biggest layers, unless you are using Windows XP. Once you've exported the image into .ico format, you can use it to replace the icon for any file or folder you'd like.  See this guide for changing the icons on your Windows computer. See this guide for changing the icons on your Mac OS X computer. You will need to use a free online converter to change the ICO file to an ICNS file (Mac's icon file format).
What is a summary of what this article is about?
Change the canvas size. Adjust the color. Create the different icon sizes. Examine your layers. Save the image as an icon. Use the icon.