How is an intimate relationship different from a friendship?What are some qualities that contribute to the success of an intimate relationship?

How is an intimate relationship different from a friendship?What are some qualities that contribute to the success of an intimate relationship?
Please don’t answer too short. I don’t understand. I am studying American Online Program at my country so this course is hard to learn and look for reliable materials. Moreover, english is not my native language. Thank you so so much all tutor.