I am trying to add a custom field (already created) to Leads that have the criteria Industry=Transportation. Can someone provide the steps to do this? Thanks in advance.

I am using the standard Lead Object, and the "Industry" drop-down that is standard to that object.  If the picklist for "Industry" is selected as "Transportation" I want additional fields to populate in the Description for that Lead. I want these additional fields to carry over if this Lead moves on to an Opportunity.