The final part of the series on creating an eCommerce website using Strapi, Jekyll, Tailwind CSS, and Snipcart focuses on implementing cart functionality with Snipcart. Initially, users need to register with Snipcart to obtain an API key, which is then incorporated into the `default.html` file for global access across the website. The code in the `default.html` file is updated to include Snipcart's CSS and JavaScript to enable the shopping cart feature. Additionally, modifications are made to the `product.html` layout to include an "Add to cart" button, which uses Snipcart's attributes to handle product details like ID, name, price, and description. This setup allows users to add multiple products to their cart, which updates automatically, enhancing the website's functionality by providing a seamless shopping experience. The series concludes with references to the final source code repositories for both the frontend and backend components.