HDR or High Dynamic Range Photography is a fairly new way of taking photos. Some people like it and others hate it.
I am no expert but I will try to explain and answer various questions.
Anyone can create HDR photos. The real way of making them is to merge a series of photos together. The photos are all exactly the same except for the fact that exposure is different.
HDR is short for High Dynamic Range. To put it simply it is a post processing method that takes a series of photos (or one single photo) and merging them to create one final image. Then a week of the contrast and tones to create something unique to make the photo pop.
The usual way is to take three photos of the same thing using image bracketing which allows you to take a underexposed, normal and overexposed photo. I have created this video to give you an idea.
You can create HDR images using just one photo and using software such as Lightroom or Snapseed.
The camera really doesn’t matter, the real work comes in the post processing. You can take a single image on your phone and with the use of software create a HDR photo. Equally a mirrorless or dSLR will have the option to image bracket and will in my opinion take a better quality photo.