As a writer you need to have imagination, and of course, stories do not have to be true. However it is best to base your story on something you know about, and set it in a place familiar to you. Don’t set your thriller in New York, or your love story in London, if you have never been to those places. The best writing can convey the smells, sounds and feel of a place which you can never describe if you haven’t been there yourself.
The same with characters: choose the kinds of people you are familiar with. And if you really want to write a story about a doctor’s life, even if you don’t know a doctor, then do your research: see if you can find out from someone who knows a doctor what kind of challenges they face, what their worries are etc. You could also use the internet to do research on things you need to know.
But don’t overlook your own environment: there will be rich stories, and characters, and events to draw on. Often your best writing will be when you are reflecting your own back yard rather than borrowing second-hand stories and settings from the movies or TV.