It is good practice to reflect on your training sessions, or whole courses. It’s quite hard to do this without a framework.
The 4 Fs is a way to structure your reflections on a training session, a programme of learning, or a single incident in the classroom.
The important thing is to get your thoughts down on paper (or on computer/tablet/smart phone). This makes you focus on it, quantify it, and helps you to learn from it constructively for the future.