This guide is based on the current version of Stackbit's supported themes. It may not be relevant if you are working against an older theme or if a developer adjusted how this process works for your site.
Though there are a number of ways to work with blog content in Stackbit, we recommend using the CMS editor to edit blog content. CMS mode is great for structure, repeatable content objects like blog posts.
How blogging works will depend on the theme you chose for your site. And it can be customized from there. Here is a video on creating blog posts with the Starter theme.