Hi Lucertola,
I know it can be difficult to follow the jargon, I remember being equally puzzled when I started doing cryptics.
A lovely surface just means that when you read the clue it all makes sense, not just in terms of grammar, but in the way it relates the story.
If you compare these two clues, one from last week and one from this week....
10a Mark a git's been given, being contrary – disgrace (6)
13a Briefly hit it off ... before he delivers trite observation (6)
The top one makes no sense whereas the second one reads beautifully.