You as an Admin, or user with the relevant permission, can decide what the sequence of a learning paths's courses will be and whether it will be optional or mandatory.
In the left navigation, make sure you are in the Academy Workspace.
When in the Academy Workspace, select Training Admin for all Training Administration options.
Select Manage Training and then select Learning Paths.
Then select the desired learning path from the list provided, then Courses.
A list of all the courses within your learning path will appear. You can change the order of the courses with a simple drag and drop.
By default the sequence is optional and the learner is free to attend the different courses of a learning path 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 learning path, 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 Learning Path Scheduler to set up a specific number of days after which each course will be available. (Read more on this process here: Using the Learning Path Scheduler