The courses are divided into units, lessons, and activities. Each unit has 5 lessons, which in turn are divided into 5 activities. The Beginning and Intermediate I and II courses are linear*; in other words, the student cannot move on to Activity 2 without doing Activity 1. These courses cover all the basic grammar structures in English, from the Simple Present to the Conditionals. The Advanced course is free; in other words, the activities can be done randomly, in any order.
* As a teacher, you are not limited by this. You can do all the courses in any order.