Workbooks – Tableau workbook files have the .twb file extension and are marked with the workbook icon.
Workbooks hold one or more worksheets and dashboards.
Bookmarks – Tableau bookmark files have the .tbm file extension and are marked with the bookmark icon.
Bookmarks contain a single worksheet and are an easy way to quickly share your work.
Packaged Workbooks – Tableau packaged workbooks have the .twbx file extension and are marked with the packaged workbook icon. Packaged workbooks contain a workbook along with any supporting local file data sources and background images. This format is the best way to package your work for sharing with others who don’t have access to the data.
Data Extract Files – Tableau data extract files have the .tde file extension and are marked with the extract icon. Extract files are a local copy of a subset or entire data source that you can use to share data, work offline, and improve database performance.
Data Connection Files – Tableau data connection files have the .tds file extension and are marked with the data connection icon. Data connection files are shortcuts for quickly connecting to data sources that you use often. It's a small XML file with various connection info this last statement is not from the manual
For more info follow the below link
I hope this may help you!
Thanks Mahfooj for all your help.