The three biggest keys to selling books are

1) Product Market Fit i.e. writing books that people want to read. That means writing books that are in a market/category/area that people are looking for

2) Offering Readers a great value proposition. For readers who have a lot of money it means great entertainment. For readers who don't have money it means great value for money. For readers who don't have much time, it means a book that is great use of their time

3) Reaching the Perfect Readers for Your Book. After you write a book that has Great Product Market Fit and Offers Readers a Great Value Proposition, you have to get it into their hands. This is the distribution and marketing and book store part

If you don't care about money and profit, then start by focusing on offering a very compelling value proposition - a very well written book at a low price

You still have to make sure you write a book in an area that has a good number of readers
You still have to find a way to reach those readers and let them know about your book

However, a large part of your headaches and troubles vanish if at the beginning (or even for the long term) you can focus on simply selling a lot of books without worrying about how much money it makes you. Go for a low and very compelling price and build up your reader base