The four categories or levels of e-learning are commonly referred to as the "four generations" of e-learning, which are as follows:

1. First Generation: The first generation of e-learning involves simple page-turner courses that are typically text-based and lack interactivity. They are often delivered via CD-ROMs or basic websites.
2. Second Generation: The second generation of e-learning includes courses that are more interactive, incorporating multimedia elements such as images, audio, and video. They often use Learning Management Systems (LMS) to track progress and completion.
3. Third Generation : The third generation of e-learning is characterized by the use of simulations, virtual environments, and gamification to engage learners and provide more realistic and immersive learning experiences.
4. Fourth Generation: The fourth generation of e-learning is still emerging but involves the use of artificial intelligence, adaptive learning, and personalized learning paths to deliver customized learning experiences tailored to the needs and preferences of individual learners.

These four generations or four levels of e-learning can somehow define whether an e-learning course matches your learning or teaching style. Each type of learning has its own pros and cons, so you will want to consult a freelance e-learning content development consultant before building your own.