How can I put pdf books on my website

Depending on the size and quantity of PDF books,  you might want to explore Amazon Web Services for storing your digital content as the cost difference is much lower than normal web hosting.  Especially if you use Amazon's S3 Buckets or Glacier data storage. 

You could sell your books through any commercial shopping cart system that redirects customers to their digital download file after their purchase is completed (WooCommerce, Shopify, etc...)

These are things you should be discussing with your web developer or online site service provider (Squarespace, WordPress, Webflow, Wix, etc...)

Good luck with your project.

Just like you upload any other files: HTML, JPG, etc.

Ask your website provider how to upload files to your space, and then put a link in your HTML code to that location

FOR EXAMPLE

I uploaded a text file to my assigned space at my ISP and created a link http://www.direct2usales.com/PrE2021.txt