Knowing how to select parts of your Gimp documents with the help of Quick Mask might be one of the first things you should learn when starting with Gimp. Let me introduce you to the basics of Quick Mask.
You don't need Photoshop or some other advanced piece of software to resize a large number of images at once. You can use Microsoft Office Picture Manager which is part of the Office suite.
Did you know you can use your camera with Adobe Lightroom to shoot photos and display them directly on your computer screen? It's called shooting in tethered mode.
CSS is a mighty powerful language for shaping your web objects. You will learn to create a two versions of a web button, one with and other without a transition.