Plans and sections can be completed in 'any' or 'sequential' order. Here we'll look at how to change these settings and what it means.
You can change the order that sections are completed by opening a template, and clicking Template settings on the main template page. You'll see an option How should sections be completed?:

Remember to click Save changes when you're done.
Any order is the default order and means that when the plan is created, all sections are 'open' and available to have tasks completed. So the participant can choose a task from any section and complete them in any order.
If you choose sequential order, sections must be completed one-by-one. So when the plan starts, the first section will be 'open' (others will show as locked until the first is completed). Once that section is completed (i.e. all the tasks have been completed), the next section will open.
This continues until all the sections are complete.
To change the order that tasks within a section are to be completed, find the section that contains the tasks, click the Manage section button, and then click Section settings.

Remember to click Save changes when you're done.
Any order is the default order and means that as long as the section is 'open' (available), then the tasks within it can be completed in any order.
If you choose sequential order, tasks must be completed one-by-one. So when the section becomes available, only the first task will be 'open' (others will show as locked until the first is completed). Once that task is completed then the next task will become available.
This continues until all the tasks in the section are complete.
By making the section order sequential and making the task order sequential for every section, the plan will be fully sequential.
This means that each task will be need to be completed one by one for the whole plan.