This is a blog I write to learn about things I'm interested in.
Read The talking bit
For local testing, use the following command:
jekyll serve --incremental --livereload
The --incremental flag only updates the changed files. Remove it if you experience problems when rendering the site locally. For example, because the index page will not update if you change the title of a post, etc.
Check Jekyll documentation for details.
In order to style the site you need to work in the assets/css folder. Jekyll will compile and move needed files to the _site/assets folder, from where it will serve them.