There are two categories of Fluid templates:
You don't need to touch first level templates. They are templates for running xBlog by its controllers only.
The setup of the content in the frontend is done by second level templates. If you like to adapt frontend output to your needs, templates of the second level empowers you.
You can include your own layout, partials and templates by the Constant Editor. See
Resources/Private/View/ ├── 1stPlugin <- don't touch this level │ ├── Layouts │ ├── Partials │ └── Templates ├── 2ndContent │ ├── Layouts │ ├── Partials │ └── Templates └── FluidStyledContent └── Foundation