How does it work?

Very simple: To create Excel templates, you only need to add mappings the same way you do with Word templates. 

${Summary}, ${ReporterUserName} and ${AssigneeUserName} are examples of mappings similar to the ones used on Word templates.

Iterations

To define an iteration, you need to merge columns and define the "for" inside of those merged cells. The same thing should be made to define the "end" of the iteration. All content between the "for" and the "end" will be duplicated for each iteration.

Functions

Differences between Word and Excel definition