I'm afraid I don't understand your question.
Student or Learner
Is the comma a abbreviation and the word but? But, changes the sentence, should there be a comma before or after the word but? Paul
I wonder if your first question should have read "Is a comma an abbreviation of the word 'but'?" If that's the case, the answer is no. A comma is a punctuation mark. It's not an abbreviation.
As far as whether the word "but" should have a comma with it, it depends entirely on the sentence.
I am short but not fat.
I like beans but I don't like lentils.
I like apples but, unless they're cooked, I don't like pears.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.