Coenzyme A is very important Enzyme that we get from Pentothenic acid . But i am not able to find a mechanism at the level of new bonds formation and destruction that could tell how exactly 

1 : Co enzyme A works 

and

2: how it is converted into acetyl coenzyme a 

3:  how acetyl co enzyme synthstase works what are the active sites that hold the substrate and co-A..

 

This is a very broad series of questions, and at least for question 2, I see several possibly answers.  For example coezyme A is converted into acetyl CoA during beta-oxidation of fatty acids but also as you imply by the enzyme acetyl CoA synthetase.  My advice is to start with a good biochemistry textbook, and you may be able to fine-tune your questions.