Hi, 

I'm new to Apex, and want to create what I think is a pretty simple cross-object field update trigger. 

An Opportunity has an Instructor Name lookup to a Contact record. When I change the opportunity record to Active, I want a custom field to update the instructor employment status to Employed on the Contact record. Likewise, when Opportunity stage moves to Ended, I want Contact status to go to Available. 

Any ideas on how I can accomplish this? Thanks very much for your input.