Explanation
According to the official Tableau documentation:
Tableau data source files have the .tds file extension. Data source files are shortcuts for quickly connecting to the original data that you use often. Data source files do not contain the actual data but rather the information necessary to connect to the actual data as well as any modifications you've made on top of the actual data such as changing default properties, creating calculated fields, adding groups, and so on. For more information, see Save Data Sources.

Explanation
According to the official Tableau documentation:
Tableau packaged workbooks have the .twbx file extension. A packaged workbook is a single zip file that contains a workbook along with any supporting local file data and background images. This format is the best way to package your work for sharing with others who don't have access to the original data. For more information, see Packaged Workbooks.

Explanation
Distribution Pane
Explanation
This is the Analytics pane! Read more from the official documentation below:

Explanation
THIS IS A VERY IMPORTANT QUESTION
To answer this question, you need to understand Tableau's Order of Operations. See below and remember this always:

Explanation
According to the official Tableau documentation:

Dimensions don't have aggregation properties, and adding properties manually each time defeats the whole DEFAULT aggregation purpose. Window tab doesn't have any default aggregation option!