For what? What "Diplomacy Actions" do, what "Treaty Maintenance" does, what % Oratory before you get to degrade treaties, how much bribe money is required, how to write treaties, how to submit treaties?
Those are fairly simple to explain because they mostly require the ability to press the right buttons and select the right options from a dropdown menu. The latter two also require about elementary school English writing skills, but that shouldn't be too hard if you are capable of playing BM already.
Now the differences between a normal diplomat and ambassador might be a bit subtler. Discussing only mechanics as is my personal policy, your diplomatic actions like praising realms has some greater effect as ambassador. It even says "Your position as ambassador lends more weight to your words" or some text to that effect. Ambassadors also are capable of signing treaties for your realm that they or their family member didn't write. Diplomats just get to write them and that's it. And that's pretty much the only physical differences between the two. Ambassadors get a special title in their signature whereas diplomats don't, as well. It looks like the following:
<Your name>
Ambassador of <Your realm>
