To enforce the order in which a Trainee must complete their Modules, you can enable the Enforce Module Sequence setting. You can enable this from the Settings tab in the Course.
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 get themselves out of the failed state by choosing to retake the module. 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.