How do I create new tabs next to the about tab and link those tabs to new posts?
Check the navbar tutorial
In the html for building your navbar you need to loop over pages in html
Here’s an example
If you use the minima theme you don’t need to write the html. Here is my project based on Jekyll new command and it uses minima. I don’t have any includes or layouts file in html - they come from the theme. If I don’t configure the header pages item in config then menu is built automatically, or i can define pages and the order for menu
Also I need to add that looping of posts is a bad idea for navbar as your navbar becomes too full after say 10 posts
Rather add pages like about and contact to your menu / navbar
The place to loop over posts with title, preview and link is on a Blog pages or your homepage
Again, you get this out the box with minima. Here is the minima file
Follow the tutorials. or use jekyll new command or click Use this Template on my repo in my previous answer so you have a working example to start with and a reference for your existing project