An LMS is the school of your e-learning program. When learners log on to study, they use the LMS software, much like students do when they walk through the door of a school. Using an LMS, students select courses, receive content, complete exercises, quizzes, and communicate with instructors and other students.
All LMS have the basic features described above.
Then the fun begins. Some LMS provide authoring tools. Some contain competency instruments that help students select courses to match gaps in their skills and knowledge. LMS can also vary in their look and feel. Some are 3D representations of learning environments, with fancy graphical metaphors for rooms and learning activities.