Layering by it\'s name tells you what it\'s all about.
But in simple terms it means using progressively smaller and lighter areas of paint to achieve a smooth highlight. ie paint a base coat and then with thinner (more diluted paint) cover 80% of the area with a lighter coat, repeat for each stage of the highlight (80% of the previous 80%) so that you end up reducing the amount of highlight at each stage until you can paint almost a pure line as the final highlight.
Since I can\'t wet-blend (and I\'ve tried!) I use layers and have found that the thinner the paint and the smaller the difference between colour gradients the smoother the effect becomes.
It might be easier to check out my gallery for some examples.