Creating a form in WordPress without using any plugin, but with Fabform, involves several steps. Here’s a basic guide:

1. Set Up a WordPress Theme: You’ll need a custom WordPress theme to add your form. If you haven’t already, create or modify a theme. You can do this by creating a child theme of an existing theme or developing a custom theme from scratch.

2. Create a Template File: In your WordPress theme directory, create a new template file (e.g., contact-form.php). This file will contain the HTML markup for your form. You can include it in a page template, post template, or create a custom page template specifically for your form.

   Here’s a simple example of a contact form:

   <!-- contact-form.php -->
   <form id="contact-form" action="<?php echo esc_url( admin_url('admin-post.php') ); ?>" method="post">
       <input type="hidden" name="action" value="submit_contact_form">
       <input type="text" name="name" placeholder="Your Name" required>
       <input type="email" name="email" placeholder="Your Email" required>
       <textarea name="message" placeholder="Your Message" required></textarea>
       <button type="submit">Send</button>
   </form>

3. Handle Form Submission: You need to handle form submission in WordPress. This typically involves creating a custom endpoint to process the form data. Add the following code to your theme’s functions.php file:

   add_action('admin_post_nopriv_submit_contact_form', 'handle_contact_form');
   add_action('admin_post_submit_contact_form', 'handle_contact_form');
   
   function handle_contact_form() {
       // Process form data here
       // Use Fabform library or custom PHP code to handle form submission
   }

4. Implement Fabform or Custom PHP Code: Within the handle_contact_form function, implement Fabform or custom PHP code to process the form submission. You can use Fabform for form validation, sanitization, and email sending, or you can write custom PHP code to achieve the same functionality.

5. Test Your Form: Test your contact form to ensure it’s working correctly. Make sure submissions are being processed as expected.

6. Styling: Style your form using CSS to match your WordPress theme’s design.

Remember to sanitize and validate user inputs to prevent security vulnerabilities such as XSS and SQL injection.