You should complete each lesson first, before moving on to homework!
Lessons introduce new concepts, LSAT question types and how to approach them. This provides the foundation of your LSAT skill set.
Homework reinforces the concepts covered in each lesson and strengthens your ability to analyze and work through specific LSAT question types. The quizzes and drills give you a chance to practice your skills and test your understanding of the methodology.
In lesson 1, you will learn about sufficient and necessary conditions.
When you move on to the homework for lesson 1, you'll be quizzed on this concept!
The homework also has explanations for the questions you complete, which are helpful when you go to review your work. Doing the lessons first ensures that you will understand the methodology and terminology being used in these explanations.