People are often intimidated by the seemingly steep learning curve with digital photography, especially Photoshop.
Just like climbing mountains, the Photoshop workflow is based on learning a few solid principles, and then putting one foot in front of the other. Pretty soon, the steps get easier and you'll look back and say, "I can't believe we were all the way down there."
I'll admit that I had no idea what "Blend Modes" or "Calculations" were when I first started. I only knew what that I wanted pixel "x" to look like pixel "y." Then I realized that essentially all Photoshop does is alter the luminance value of individual pixels (Although at times it does that using some complicated calculations using complex algorithms and formulas). With that understanding, and based on the following two principles, all the tools, functions, and options will start to make sense.
So what are those essential principles?
All you have to work with are tones. The things in your pictures are not really things at all. They are simply tones that are different than other tones (another word for luminance value). That differences in tone is what we call contrast, which we then interpreted as shape and texture. We then recognize those shapes and textures as resembling things in the environment and therefor think of it as an actual thing.
By Altering the difference between one tone and the next adjacent tone you create a "contrast." The more the difference of those tones, the greater the perceived degree of contrast. We can call this "separation" "definition" "clarity" "sharpness" etc. The word to describe it can be different depending on the task and what we want to affect, but what we are really working with are the differences between tones.
With that understanding we can then talk about how we can alter the tones to create the pictures we want to make. All the tools in photoshop begin to make sense when viewed as methods of changing the differences between two adjacent tones. The beauty of Photoshop gives us a fairly intuitive interface to do so, and that we don't need to know all the algorithms or formulas. Only the effects they have on the differences between tones.
In future posts I will start work through the different ways you can make those changes and point out which steps to take for certain similar situations.