Conga Composer has the unique ability to use data from a Salesforce Report (or Conga Query) as detaildata (e.g., invoice line items for each invoice). Since you can retrieve multiple rows of data, we need a way to designate an area on the template that can dynamically grow to accommodate an unlimited number ofdetail rows.
To solve this, we've created Detail Regions. Detail Regions let you identify a portion of your template that can dynamically grow.  Merge fields, along with any other text, placed within a Detail Region will automatically repeat for each row of detail data.
In PPTX templates, you can define a Detail Region by using a Table, a Group or a Slide.  This article describes using a table

Using a Table

For arranging data in columns and rows, you'll find Table-based detail regions particularly useful.  You create a table including column headers and a row to hold your merge fields.  Conga will automatically expand the table to accommodate the number of rows in your dataset.
Here’s how:
  1. In your PPTX template, create a table with at least two rows (one for column headers and the other for merge fields) and as many columns as necessary to accommodate your data.
  2. In your Template Builder window, locate a field from a dataset that may contain multiple rows of data. Click the field name to copy it to the clipboard.
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  1. Switch to PowerPoint and move to the first cell in the row that will contain your merge fields. 
To mark the beginning of the Detail Region, create a merge field with the name{{TableStart:DatasetName}} where DatasetName corresponds to the name of the dataset from the Template Builder window.

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  1. To mark the end of the Detail Region, move to the last cell in the row and create a merge field with the name {{TableEnd:DatasetName}} where DatasetName corresponds to the name of the dataset from the Template Builder window.
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  1. Between the TableStart and TableEnd fields, place merge fields that correspond to the fields of your report data. These merge fields will be populated with data from the first row of the detail data, then the whole region will be repeated, the new fields will be populated with data from the second row, and so on.
Here's the completed table:
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Here's the output from Conga:
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Important: A slide may only contain one set of TableStart / TableEnd fields
Tip! Change the color of the TableStart and TableEnd fields to help visually distinguish them from other merge fields.  We suggest red.
Important: Use “simple” field names within Detail Regions. Do not include DatasetName to refer to the dataset since the dataset is identified by the TableStart field.
Please follow these guidelines when creating a table-based Detail Region:
  • A slide may contain only one detail region
  • If you have more rows of data than will fit on a slide, new slides will be generated to accommodate your data
  • PowerPoint does not have the ability to perform calculations (like =SUM(ABOVE)), so please use a formula field in Salesforce to perform calculations and merge the result into the table
  • PowerPoint does not support images within cells.  If, however, you include an Image: merge field, the Conga will apply the image to the cell background.  See the section on Images for more details.)
  • Do not use the “formal” field naming convention within tables, i.e., do not reference theDatasetName