what are these drag drop fields

Hello,
 
Thank you for your question.
 
The majority of capabilities of Flexmonster are described within the documentation.
 
Answering your questions about placing values and its aggregation:

1. Putting values in rows and columns affects only their data representation. Adjusting the way the data is presented provides a better understanding for the final user. The slice of the data to be shown can be flexibly adjusted through UI using the Field List. Also, it is possible to drag and drop the field from the column to the row and vice versa. The default slice is controlled with the slice object of the report you pass to the component. More about the slice object can be found following the link.
2. Adding additional fields to the row or the column allows seeing the detailed information about the specific measure. For example, there is a field named "Category" in a column, "Month" in a row, and "Revenue" as a measure in the current report. The data displayed at the intersection of the specific category and month will present an aggregated value of all fields of the data set, even if they are not displayed on the component. Values aggregation by default is their sum. That is why in case you have an undisplayed field "Customer" representing companies, the value at the intersection presents the revenue from all customers for the chosen category and month. In case the user requires information about revenue from the specific company, the "Company" field should be added to the row or the column.
3. The last row, named "Grand Total", represents the total value of the measure for all hierarchies. According to the example above, the grand total would display the sum of all revenues from all customers for all categories and for all months.

 
More general information about pivot tables can be found by the link: https://codeburst.io/pivot-table-core-concepts-web-solutions-177d1f08e96e.
 
We hope it helps.
Feel free to contact us in case of additional questions.
 
Kind Regards
Illia