Harry Potter and the Portal of Darkness

Harry is beginning his sixth year at Hogwarts School of Witchcraft and Wizardry. Voldemort is back in full power and the wizarding community knows about it. After hearing the prophecy in his fifth year, Harry now has to face a year knowing that it is kill or be killed. After the death of his godfather, Harry is in a state of depression and shock. Will his friends be able to pull him out in time and is he really the one in immediate danger? Is one of his friends more important to him now than he has ever noticed before, and is Harry the only one who see's this? Will Voldemort attack him while he is at school and what exactly is the portal of darkness? Does it have anything to do with the veil in the department of Mysteries in the Ministry of Magic?