There are many degrees of realism in art, from almost photographic depictions to very simplified, abstracted, but still recognizable interpretations.
Most of my students know my work before they take my classes, so they expect to be taught how to paint in a more or less realistic style.
However, style cannot be taught, it has to be conquered by years of work.
What I teach is how to get there:
First, an understanding of color and its three properties: Hue, Value and Chroma, and second, how to truely see and observe: How to use what the right brain senses and what our eyes see, to create on the canvas, through a pattern of shapes and colors, the image exactly the way we want it to look.
Knowing or seeing every detail of the subject is not only unnecessary for the painter, but often undesirable. The left, logical side of the brain interferes in such a way that it blocks the right side, which is more creative. What we know (or think we know) gets in the way of real observation and without real observation there is no true realism.