1. Setup the Backend: This involves setting up a server that can handle requests from your front-end, manage user data, manage product key data, and facilitate transactions. You could use Express.js (a Node.js framework) or Django (a Python framework) for this.

2. Design the Frontend: This involves designing the user interface of your shop. You'll need to design pages for displaying your products, user registration and login, cart functionality, and payment. You could use HTML, CSS, and JavaScript (perhaps with a framework like React or Vue.js) for this.

3. Database Management: You'll need a database to store your product keys, user data, and transaction data. You could use MongoDB or SQL for this.

4. Payment Gateway Integration: To handle payments, you'll need to integrate a payment gateway like Stripe or PayPal into your website. Both these services have extensive documentation to guide you through this process.

5. Secure Delivery of Product Keys: Once a user has made a purchase, you'll need to deliver the product key to them in a secure manner. You could do this through email or through a secure user dashboard on your website.

6. Security: Make sure all data is encrypted and secure, use HTTPS for all connections.

7. Testing: Test all aspects of your site to ensure everything works as expected.