a concept map (care map) is still a care plan. it is just presented in a different format than a chart/column form. you still need to follow the five steps of the nursing process to complete this assignment. if this is not a real patient, then what you need to do for step #1, the assessment is to list out all the signs and symptoms of diabetes mellitus. you should be able to find them in any textbook and plenty of websites on the internet. from those symptoms you move on to step #2 which is to group some of the symptoms into nursing diagnoses. you need a nursing diagnosis reference book to help you classify the diagnoses correctly. step #3, developing the goals and interventions, is based upon those signs and symptoms of the disease.
you can find information on care planning and choosing nursing diagnoses on these websites:
again, let me stress that the only difference with a concept map is how you are going to put all this information on a piece of paper. you are still going to go through the steps of the nursing process.