Explanation
In Tableau, a story is a sequence of visualizations that work together to convey information. You can create stories to tell a data narrative, provide context, demonstrate how decisions relate to outcomes, or to simply make a compelling case.
A story is a sheet, so the methods you use to create, name, and manage worksheets and dashboards also apply to stories (for more details, see Workbooks and Sheets). At the same time, a story is also a collection of sheets, arranged in a sequence. Each individual sheet (worksheet or dashboard) in a story is called a story point.
When you share a story -for example, by publishing a workbook to Tableau Public, Tableau Server, or Tableau Online-users can interact with the story to reveal new findings or ask new questions of the data.

Explanation
For Standard Deviation and Variance, we don't need to use quick table calculations, since they are available by default. See below:

However, as seen in the types of quick table calculations available in Tableau, Rank and Moving Average belong to only this category.

Explanation
When you connect to a new data source, Tableau assigns each field in the data source as dimension or measure in the Data pane, depending on the type of data the field contains. You use these fields to build views of your data.

Explanation
It is possible in Tableau to use a sheet within a story directly.
Moreover, in Tableau, a story is a sequence of visualizations that work together to convey information. You can create stories to tell a data narrative, provide context, demonstrate how decisions relate to outcomes, or to simply make a compelling case.
At the same time, a story is also a collection of sheets, arranged in a sequence. Each individual sheet in a story is called a story point.

Explanation
Presently, there is no official way to connect your data in Firebase directly with Tableau Desktop.
A workaround however can be to export your Firebase data into Google BigQuery, and then connect it to Tableau Desktop.
But then again, it is a workaround and not an official out-of-the-box solution.
The following are the available Data sources available as of now:
* Server
* File