Hello,Ms.Helena
You have to options to transfer between Chongqing and Dazu: railway and long-distance bus.
take train from Chongqing Caiyuanba Railway Station to Dazu (Youtingpu) Railway Station through Cheng Yu Line.
take long-distance bus from Caiyuanba Long Distance Bus Station (or Chenjiaping Long Distance Bus Station) to Dazu.
From Dazu to the sights, you can either walk, take a taxi or take special line minibus.

Crucian is a specialty of Dazu, have a taste. And you are suggest to stay at Nong Jia Le (农家乐) for one night or two.

Enjoy~~