I need to create a column that subtracts the date in this column from the date in another column to get the number of days between the two dates.
Put just a simple - between these two fields. 
Example:
Formula Easymorph.morph (3.6 KB)
Thank you sir.
"Is there a way to create a column with a default date value as the last day of the current month?"
You can use a formula like monthend(today()) .
Sweet. Thank you sir 
Just use the aggregate action.
You should go through the tutorials EasyMorph | Learn how to transform data
The action is described in the first chapter "basics".