"I'm sorry"

"Sorry," an expression of regret or condolence - as per Wikipedia's definition.

Do you say it after you possibly upset someone? Do you say it when you have upset a person? When you've done something wrong?

What happens when you did nothing wrong and you want to hear such a simple term? How do you approach the person?

Should a spouse be responsible for another spouse? In terms of spouse A doing something - while NOT in the presence of spouse B - does spouse B still get in trouble for what the other spouse did? Should spouse B say "I'm sorry for spouse A's actions" or would it be spouse A's thing to do?

What happens after a person says "I'm sorry" - it doesn't always make things right. In the event of it nothing making things better what is the time frame to allow things to heal over or pass? Does it all depend on what has happened?

What if a person was so rude they don't understand they should even say sorry?