How do you become a writer?
There is no one way to become a writer. So, let me list a few ways.
First, I would say that you will need to write a lot to become a good writer. As they say practice makes perfect.
Second, you can major in a subject in college that deals with writing. For example, you can major in English or history. Also you can be a part of the school paper. Some college have great school papers. you can even do this in high school.
Third, you should start submitting your work to various peer groups. The most feedback you get, the better you will be.