Question

What's the difference between an Ambassador and a Moderator?

Answer 1

You could compare the ambassadors with a welcoming committee, and the moderators with the police. 2 totally different things.

Ambassadors are here to guide the new users and show them the ropes on how to use the site. You can recognize them with the Purple Ⓐ next to their name.

When you violate the Code of Conduct. The moderators will take action. They can warn people and suspend then when they don't listen to warnings. When you see someone misbehaving, click the report abuse button and the mods will take a look at the problem.
You can recognize moderators by their purple names (as you can see by looking at my name) and purple ring around their profile picture.
courtesy @thomaster

Answer 2

Oh okay. :)