Even though we spend a substantial portion of our life studying or working, most of us have not been taught how to do so in the most effective way. Learning should not imply just reading a text several times and then repeating it.
Learning implies three basic actions: exposure to material, revision and practice.
There are many cognitive processes involved in learning (short and long-term memory, attention span, executive functions, perception, language, etc.).
The best way to learn is getting to know all these processes, their limits and some strategies to make them work in the best and most effective possible way. This is called metacognition.