Like its federal counterpart, the MA constitution is the primary governing document for the laws of Massachusetts.
The constitution is published in the Massachusetts General Laws and is also available online.
Session laws are those laws enacted by a legislature during one session. They are published chronologically in bound volumes, and are also available online. This publication in Massachusetts is called Acts and Resolves. Some of these laws are eventually codified into a code called the General Laws of Massachusetts; here, they are arranged by subject for easier research. There are also two commercial versions of the Code, which include many helpful annotations to assist you in your research.
The annotated versions can also be found in WestlawNext and Lexis Advance.