Think of Padding as the space used to cushion each of the elements in your post. There is just one padding setting and it will be applied around each element of your post for a consistent and uniform aesthetic.
The padding setting is in the horizontal toolbar at the top and can be changed through the drop down.
Example of change in padding:
If you're seeing any extra padding on your published posts (for example there's extra space under full width images), it's likely coming from your websites CSS settings.