Typically, filing an unemployment compensation claim is the first action required during layoffs.
See the list of state offices published on the United States Department of Labor's (DOL) website to find contact information for the agency in charge of unemployment compensation in your state.
Be sure to verify exactly what is expected of you when you are approved for benefits so that you will not experience any problems, such as an interruption in benefit or unexpected loss of eligibility for unemployment compensation.
If you are out of work for a while, you may want to apply for financial assistance programs beyond the scope of unemployment compensation.
You may also find out just how much unemployment compensation you will be able to collect between jobs depending on how long you were with your current (or if you've already been laid off, former) employer and what your current salary is.