Excel templates are used to produce lists and charts from data held in the Common Data Service. They are used with a list of records in a view.
You can create an Excel template from any view. In the following screenshot, you can see the options you get when you click the Excel Templates button:

To create a new template, click on Download Template and the following window will appear:
You select the entity and view you want to use, and an Excel document will be downloaded to your computer. You can then edit the Excel document, where you will have full formatting, formulas, and charting available.
Once you have created your Excel document, upload it by clicking on Excel Templates, selecting...