Slip laws are individual copies of laws published as soon as they are enacted.
Cite to a slip law if the law is so new that it has not yet appeared in the session law compilation or statutory code for the relevant jurisdiction. Usually you will cite to a code or session law!
Federal slip laws may be cited according to Bluebook Rule 12.4(a). Even though they haven't yet appeared as session laws in the official Statutes at Large (see Session Laws tab), new federal statutes are assigned a Stat. citation that may be included.