Hi bvzastrow,
Those are Custom Investment Properties and you can define them under "Options / Custom Investment Properties...". You can't put multiple other fields in there and do math on them, they are just properties of a number, date, or text. See "Help..." in that dialog for details.
To be able to do math on existing fields you will want to use
user-defined fields in a Custom report. This does require the Professional or Advisor version. It isn't available in the Personal version.
To see an example of how to use Custom Investment Properties and User-Defined Custom Report fields to track expense ratio/cost, see
this.