So, you are planning to have your online bookstore but you don't have enough capital to start buying books from supplies. I don't know whether you have heard this news or not but you can make money by selling books that the largest online store in the world, the Amazon.com, also sells. It is not difficult to sell Amazon's books.
First you need to sign up for an account in Amazon.com as member of Amazon Associates. When you have signed up, you will get an account where you can use your email and password to enter the Associates Central webpage. On the upper part of the page there are widgets or astore link which you can click to start choosing the products that you are interested in selling. You can choose the aStore Widget or Omakase one. If you click the Omakase widget, you will sell products that are contextual to the content of your blog or website. You need to have a blog or website to sell Amazon's books or other products through Amazon Associates program. At the bottom of the Omakasi Links webpage, you will see the html code which you have to copy and paste inside your blog.
If you don't know how to set up a website. You can start a blog from blogger.com. As part of Google, blogger.com has special cooperation with Amazon.com which helps publishers or bloggers to sell Amazon products directly from the blogger's New Post webpage form. If the Amazon Associates account has been activated in your blogger's account, you can see it next to the New Post form. You can click the link, image or link + image to start selling Amazon's products. If you still do not understand what I mean, just check the Amazon's products that I promote in this post.
Also read: Starting an online bookstore as member of Amazon Associates