Updating a Subform with data from the main form...

Updating a Subform with data from the main form...

So, I'm a beginner with Zoho---a real beginner.   Can someone please walk me through how to populate my subform with data from a main form?   

Main Form:  I have an "airline name" field and "media area" field. 

SubForm:  I have an "airline name" and "media area" field.  When I use the dropdown in the main form to select the airline or the media area, I want the same information to update in my subform. 

Thanks for any help you can give.

DZ