A Flexible Spending Account allows you to pay for your out-of-pocket medical, dental and vision expenses on a pre-tax basis. You can elect up to the IRS maxiumum each year for your known medical, dental and vision expenses, which is about a 30% savings to you.
You do not need to be on your Employer's medical, dental or vision insurance to join the FSA. The FSA can be used for yourself and your dependents.