HDR is a function on most if not all smartphones these days. What exactly is HDR? HDR stands for high dynamic range and it's a composite of a series of images that are shot at different exposures from dark (underexposed) to light (overexposed) and balanced. When combining the three images, it provides a dramatic image with awesome shadows and highlights. The key to getting HDR images correctly is understanding when it is and when it is not appropriate to use the HDR setting on your smartphone.
The key to HDR is to finding the right balance for creating an amazing and awesome image to that of an overblown, oversaturated image. The grey line can be really thin. Keep in mind that these are not hard reasons why you should or should not use HDR and it's a matter of taste. Use this as more of a friendly guide.
Usually, to enable your HDR on your smartphone it just takes for you to open up the built-in camera app. Of course, this depends on your phone's make and model. In general, the setting is not hard to find. Also, HDR may have different names per make and model (which is petty if you ask me). Some call it “Rich Tone” or “Dynamic Tone” or even “Drama.” Your phone's manual or the brand of phone's blog can direct you to the HDR setting if they've made it impossible for you to find.
You can also buy a third party app in the App Store (iOS), (Android), and Marketplace (Windows).
Here are some recommendations:iOS: Pro HDR* vividHDRAndroid: HDR Camera+ * Camera HDR StudioMarketplace: 4Blend HDR * HDR Photo Camera
*Indicates the highest recommendation from mobile photographers in the Instagram community
Use HDR for Landscapes
Large landscape photos usually have a lot of contrast between the earth and sky. It is difficult for many cameras but especially for smartphone cameras (small sensor being the main culprit) to capture the distinct difference in contrast. When you use HDR for landscapes you will be able to get the details in the sky without compromising the earth/land by it becoming too dark. This also works for the opposite where you can capture the land without blowing out the sky. Again, with HDR you get the three different exposures; dark, light, and balanced. This helps extremely well with the subjects are so starkly contrasted.
Use HDR for Portraits in Sunlight
Lighting is one of the most if not the most important part of photography. Again you are painting with light. When the sunlight is harsh, it can cause dark shadows and glares that are really not aesthetically pleasing. HDR can help in that situation. For instance, if your photo is dark due to too much backlight, HDR can brighten up the foreground without completely washing out the well-lit spots in your images.
HDR can also make your images look crisp and color richer.
Use HDR in Low Light (No Flash)
This goes hand in hand somewhat with the harsh light scenarios. It is the similar concept of having too much light (see above) and having not enough light. Combining the three HDR images helps in capturing the shadows, highlights, and details that otherwise will get lost when taking a single image.