Every added element/tab needs to be placed here. After that, replace the placeholders (/) with underscores (_) in the href. Another detail is that there shouldn't be any repeated elements, for example:
<a class="w-full flex items-center p-1 hover:bg-[#0000000A] transition-colors w-full rounded-md" href="introduction">
<i class="fa-solid fa-book-open pr-2 w-6"></i>
<span>Introduction</span>
</a>
The first element in the content of a post is always the title. This is so it appears at the top and matches the text in the sidebar. For example:
# Main
This is a example of article in Markdown format, you can add content, lists and **emphasis**
Apart from that, there's nothing more to say; Markdown functions the same as on any typical site.