You as an Admin or user with the relevant permission can decide what the sequence of the curriculum's courses will be and whether it will be optional or mandatory.
To apply sequence changes to your curriculum's course sequence, click on the Manage Curriculum option under your preferred curriculum and then select Courses on the left panel. Finally, under Courses click Edit Courses.
The list of all the courses within your curriculum will appear. You can change the order of the courses with a simple drag & drop. Moreover, Schoox allows you to decide whether the sequence of the courses will be mandatory or not.
To do so, adjust the Course Sequence setting.
By default the sequence is optional and the learner is free to attend the different courses of a curriculum in any order. However, to make the sequence mandatory, just check that option in the Courses Sequence setting.
Please note that if you have added optional courses to your curriculum, you will have the ability to skip optional courses and move on to mandatory training.
Apart from defining the sequence of your courses, here you can also use the Curriculum Scheduler to set up a specific number of days after which each course will be available. (Read more on this process here: How to use the Curriculum Scheduler?)