When you add multiple modules to a course, your trainees will be guided through the course in the order you have set. However, unless you enforce module sequence, trainees will be able to jump into other modules in whichever order they'd like.
You can force them to complete the modules in the order you choose from the Settings tab on the Course page. Click 'Edit' and check the box next to Enforce Module Sequence on the Modules card on the Course settings page. Click 'Save'.
Courses that have an enforced Module sequence can also require a trainee to pass each module before being able to move on to the next module in the course. In this case, if a trainee fails a module the course will automatically be put into a failed state. They will not be able to proceed in the course until the failed module has been reset and the passing requirements met. If the trainer has allowed the trainee to retake their module, trainees can reset themselves from their trainee dashboard. Once they pass the module they are able to move to the next module.
To require your trainees to pass each module in the course go to the Settings tab of your Course. Next, Click "Edit".
Under the "Modules" section, check mark the "Require passing score in each module to proceed in course." option.