There are a few resources that provide access to primary law. These are valuable as they compile these resources for you.
The Naturalization Clause below specifically deals with issues of immigration law, but it is not the only constitutional provision.
The Federal Immigration Law statutory scheme is quite vast and robust, and it spans many titles. Title 8 is the most relevant, but others touch on tangential issues.
The regulations below are used to implement the federal statutes at the agency level.
Case Law is different when researching immigration law, as most cases begin at the administrative level. The judicial branch can only hear cases after administrative relief has been exhausted. For cases that make it to the Court of Appeals, typically they have been issued a final order by the Board of Immigration Appeals. These cases can be found using the sources below or on AILA Link.