Writing is magical and whether your hope to become a published author or just write for the sheer joy of writing the best way to start is to write. Just put your thoughts on paper. Try to write something every single day to get in the habit of writing. When, where, how, or what you write doesn’t matter at this point.
If you want to be a published author you will need to spend time learning about what it means and what steps you will need to take to realize your dreams.
What genre do you want to write?
Once you determine your genre or genres (I refer to myself as an eclectic author as I write in several genres) you should learn as much about that genre as possible. What is the market for this type of book? What are the required word counts? Will you set a goal for completion or just write whenever the mood hits you? Once you have an edited and polished manuscript then you can make a list of agents and publishers who you believe might be interested in your book. This takes time and effort and patience.