A veneer - that’s all there is to it (6)
I believe the answer is:
finish
'a veneer' is the definition.
(thesaurus)
'that's all there is to it' is the wordplay.
'that's all' becomes 'finis' (I've seen this in another clue).
'there' becomes 'h' (I can't justify this - if you can you should believe this answer much more).
'is to it' means one lot of letters go next to another.
'finis'+'h'='FINISH'
Can you help me to learn more?
(Other definitions for finish that I've seen before include "curtains" , "Deal with" , "Terminate, conclude" , "Come to an end" , "Refinement in social graces" .)