A paper and a pen is enough to write endless pages on anything. They're some people that write books of feelings, some writers whether they are professional or not can get you deep down in your feelings and make you feel a type of way that you've never felt before.
Writers mostly base there writing on what they've been through. Things they've experienced. Not necessarily do they based on them, they could write something their friend or family member has experienced or something they've heard online. Writers are creative, give them anything and they'll come up with something that will make you understand whatever the topic is.