When you create tasks in your own workbook on Write & Improve, you get two choices. These choices affect what kind of score you get for your writing, but they also decide how Write & Improve analyses your writing. It is important to choose the correct New Task type for your task.
If you are studying for a Cambridge exam such as Proficiency (CPE), Advanced (CAE), First (FCE), Preliminary (PET) and Key (KET), or if you want to practise the kinds of essay topics and genres that you see in these exams, or to create tasks like the ones in the W&I Beginner, Intermediate and Advanced workbooks, you should click on the CEFR button. Your writing will be assessed according to the correct criteria for those types of essay. You can find out more about the CEFR here: http://help.writeandimprove.com/frequently-asked-questions/what-do-the-levels-mean-and-what-is-the-cefr
If you are studying for the IELTS Academic exam and want to create tasks that are like the tasks you find in that exam, you should click on the IELTS button. Your writing will be assessed according to the correct criteria for the types of essay you need to write in the IELTS exam and you will get a score on the scale used in IELTS exams. You can find out more about how the IELTS exam is scored, here: http://takeielts.britishcouncil.org/find-out-about-results/understand-your-ielts-scores You should only choose this option if you want to practise for the IELTS Academic exam. Also, you will need to subscribe to the +Test Zone premium feature as the IELTS workbook and the ability to create IELTS tasks of your own is not free. If you click on the IELTS button, you will be taken to a page where you can buy a subscription.
It is very important to choose the correct task type for your needs as Write & Improve will give better results if you do.