One answer only. One answer only. Evil is a result of people turning away from Allah and his message. It comes from ourselves rather than from any outside force. If people give into evil they will go to hell.
Life is a test.
Allah gave people Islam to show them how best to care for the world and themselves. He allows Satan to tempt people away from the truth. Those who pass the test go to Paradise. Suffering and evil come from Satan. Allah allows this although He knows it is not our fault that we are weak.