I seem to be confused on how to work with and develop a Default template. My goal is to develop an overall look and feel of a default template then tweak the look and feel for the Home page or Blog page or whatever page needs to be tweaked. What I am finding is that the Default template looks to be disabled and I am having to select each template individually (Home - Page - Blog - Post - 404 Text - Default) when making any changes. The Default template or view looks to be disabled which is confusing (attached image).
I must be doing something wrong but what view or template do I need to be viewing so that I can develop and make changes to an overall default template?