Thank youuuu I finally start understanding how it works. I'm not good at Node.js and js Frameworks. But I'm an expert JEE and web architecture. I wish that I could catch up..
I found the answer https://docs.nodebb.org/en/latest/themes/templates.html
<!-- BEGIN posts -->
<!-- IF @first -->
<h1>Main Author: {posts.username}</h1>
<!-- ENDIF @first -->
{posts.content}
<!-- IF @last -->
End of posts. Click here to scroll to the top.
<!-- ENDIF @last -->
<!-- END posts -->