Documentation on using Blog System
The reason for naming the primary blog post file index.html is because there might other html files that you would like to link to/ or imbed using the curly brace/percent include file.html jinja syntax.
Go to create_post url:
Then you will need to upload a compressed/zipped file with an index.html as the root post. There can be other urls and a folder with images.
Here are other urls that will help: