刘娜... the word "stressful" is an adjective and it describes the noun, e.g., The exam is stressful / I have a stressful job (the job is full of stress). The word "stressed" is used when we are talking about how a person feels, e.g., Before the exam, I feel stressed. So, in a very simple way: things are stressful (exams, your life, your work, traveling in China during the Spring Festival) / and people feel stressed.