Hi
@Raja
So assuming you already have a defined collection (I.e. a collection with field name(s)) the 2 steps you would follow are:
1) use the ‘Add row’ action which is part of the Collections internal business object specifying your collection name as the input value.
2) use a calculate stage with your data item as the Expression and the collection field name as the store in value. Syntax for Collection field name is: CollectionName.FieldName or you can just drag the field from the Collection section on the right hand side.
So that will populate the collection, and what is it you want to do with it in Excel?