You’re writing on Facebook. This is writing. You are a writer.
Do you want to write a book? Then write a book.
Do you want to be published? You can use Amazon self-publishing.
Do you want to be a money-making book author? Then you have to market yourself. That might be the hardest part, and why so many authors have agents. It’s a common problem.
I could never edit my own stuff and self-promotion is hard. If I wanted to be a money-making author, I’d need editors and an agent.
Specificity to your goals helps you figure out what questions you need to answer.