Think of the tasks page as your own personal to-do list. Each task should have a name and short description, and it may have documents associated with it too.
Tasks may exist on their own, but they are often more helpful when you nest them into specific projects. You can create a new task from the projects page, or you can go to the tasks page and assign the task to the desired project from there. Here's what that looks like.
Once you've made a few tasks, you can get to work with documents assigned to each task. You can create a new document while viewing a task, or you can add an existing document to a task using the document editor. Any documents associated with a task will have time tracked and logged in the tasks section.