Maryam,
Here is how I would build this:
- create 2 entities - one for each of the imported files containing the columns in each spreadsheet
- create a third entity which will be used for the comparison
- use Excel Importer module to import the contents of both files into the entities you have created
- create a microflow to compare the two files and populate the third entity with the results of the comparison
- create a page with a datagrid displaying all rows in the third entity. Add an export to excel button to this datagrid to export the results
- if you need to export something more formatted, or via a background job, you could export the information in the third entity with the Excel Exporter module from the Marketplace
This is a high level description of how to address this task. You can find documentation for Excel Importer, Excel Exporter and related modules in the Mendix documentation
Hope that helps,
Mike