First, you need to register on CLEF website at: http://clef2017-labs-registration.dei.unipd.it/ 

Second, you need to join the mailing list for the Task(s) you are interested in http://clef2017-labs-registration.dei.unipd.it/ .

Task 3: Patient-Centred Information Retrieval Task Only:
Third, you need to get access to the dataset (see the dataset section of the Task 3 page for details).