The Puppet Warp tool is one of the most powerful methods to manipulate people, objects, or whatever you please in Photoshop. If you want to learn how to stretch, bend, or contort your subjects, give this helpful video a quick viewing!
Coming to you from Jesus Ramirez of the Photoshop Training Channel, this tutorial introduces you to the Puppet Warm tool, which is a powerful and intuitive feature of the program. While most people normally think of the it for subtle adjustments to a person or creative distortions, it's much more versatile than being limited to just human subjects. When you're first working with it, I personally recommend setting the mesh density to the finer setting and leaving the mesh visibility on so you can see exactly how the points interact with each other and gain a better sense for how to get the results you want. Just be sure not to overdo it with adding points, as you'll start to get some bizarre results. Lastly, make your selections carefully, so you don't end up dragging parts around that you wish to remain static.
And if you'd like continue learning the basics of photography, be sure to check out "Photography 101: How to Use Your Digital Camera and Edit Photos in Photoshop!"