With Stastic, you can create a new website or install the editor on an existing website (see the section “[How to install Stastic?]”). In order to edit the content of your website you will want to access the “admin” or “editor”.
This is very simple: simply open your website and add /admin/after its address. For example:
https://my-github-name.github.io/my-project/admin/https://www.my-website.com/admin/
Also you may find the section “[How to access my website?]” interesting.