You will find that there are dozens of different tutorials available online, ranging from books and courses that you can pay for to tutorials and video lessons that can be downloaded for free. Each of these courses is broken down into sections that will address each of the different sections of formula so that you can learn them in groups. This tends to make it much easier to fully grasp the necessary formula for each section before moving on to the next segment.
Depending on the size and complexity of the picture, and the size that you are re-creating it, this type of project can be considerably faster than the old-fashioned oil painting or watercolor, and may be more impressive to certain groups of people. Digital art buffs are become more and more the norm in the art world, and this genre is helping to get people into something they may have otherwise ignored, all because of how it was created.