The system gives two different scores. Look at the image below. The red circle shows the score on the CEFR scale.
This is the scale Write & Improve uses to measure progress and is also what Cambridge English uses to mark their English exams. You can find out more about the CEFR scores here: https://help.writeandimprove.com/frequently-asked-questions/what-do-the-levels-mean-and-what-is-the-cefr
The score shown in a blue circle is the ‘Prompt relevance’ score, from 0 to 5. This score represents how completely Write & Improve thinks you answered the question - did you answer all parts of the question, is everything you wrote relevant to the question etc. So, 0 is the lowest score for this and means your answer was not at all relevant to the question. 5 is the highest score and means you answered all parts of the question and everything you wrote in your answer was very relevant to the question.