Modifications should only ever have to be made in the /_posts/ and /_tags/ directories under normal circumstances.
To add a new post, create a file with the name structure YYYY-MM-DD-simple-name.md and insert into it the following header:
---
layout: post
author: your-name
title: The post title!
description: Something descriptive
summary: Something short
tags: [any, tags]
usemathjax: true
---Replacing the relevant fields as necessary.
If you wish to tag a post with a tag that does not currently exist in /_tags/, create a new file for the tag
named exactly the same, such as blog.md for the tag blog, and insert into it only these lines:
---
layout: tag
tag: tag-name
---Again, replacing the tag-name as necessary.