How specific should an Area of Focus be?

I recently feel really confused of the difference between a project and an AoF. Let me give an example, I have a goal to pass the CATTI2 test (a translation certificate). There are two subjects in this test, translation test and English test. I’m now really confused about whether these two subjects are projects or AoFs. I have read both the book and the installation guide for several times. But I am still not sure the difference. Can anyone share with me how do you do with a test preparation through GTD and OmniFocus?

I recommend using parallel or sequential projects for things with a defined outcome and single action lists for ongoing areas of responsibility. If multiple projects are required to achieve a larger goal, you could create a folder with a name that articulates the larger goal as a container for specific projects.

For example, you could have a folder called “🥅 Obtain CATTI2 Certification” (I added the emoji prefix to distinguish this from folders like “Health” that represent areas of focus) and place more specific outcomes, in the form of parallel and sequential projects (e.g. “Pass English Test”) in this folder.

One caveat is that you can’t mark a folder complete. But you can change a folder’s status to “Dropped” once the goal has been achieved.