Explanation
The icon shown is used to add a new Dashboard! From the official documentation:

Explanation
The following is the official documentation for the String function LEFT:

Explanation
It is possible to open a Tableau support case by visiting the following link :
https://www.tableau.com/support/case

Explanation
TWBX is all in one. It contains viz, info needed to build the viz, and a copy of the data source. It doesn't contain extracts of the data but can contain both live and data extracts. Best if want to eliminate the barrier of data access.
Create a .twbx with file-based data sources
1) Select File > Save As.
2) Specify a file name for the packaged workbook in the Save As dialog box.

3)Select Tableau Packaged Workbooks on the Save as type drop-down list.
4) Click Save.
5) The default location is the Workbooks folder of the Tableau repository. However, you can save packaged workbooks to any directory you choose.
The following files are included in packaged workbooks:
--> Background images
--> Custom geocoding
--> Custom shapes
--> Local cube files
--> Microsoft Access files
--> Microsoft Excel files
--> Tableau extract files (.hyper or .tde)
--> Text files (.csv, .txt, etc.)

Explanation
Cluster analysis partitions marks in the view into clusters, where the marks within each cluster are more similar to one another than they are to marks in other clusters.