Start by creating a new jekyll site by using the codespace and executing:
jekyll new blog
Then navigate to the blog folder and serve the site
jekyll serve
This should build and start the website on a port which can be opened
Go to the _posts folder and add a new .md file, add this as contents:
---
title: Hello!
layout: post
---
# Hi there 👋
See that is dynamically refreshes
Commit the newly created pages
Go to GitHub, settings, pages and see that there is a workflow.
The action should build and deploy. It will output a location to find the site.
Add more pages, or alter the _config file to see the effects.