MIAMI (AP) — In less than three months, uninsured Floridians will be able to purchase medical insurance online under a new federal health law. Making sure average citizens understand how it works will be a Herculean task accompanied by a massive marketing blitz promoting the biggest expansion of the social safety net since Medicare. Hundreds of thousands of Florida residents making less than $48,000 a year will be eligible for federal money to help purchase their own insurance through online health exchanges under the Affordable Care Act. The new marketplaces, which are open for enrollment this October, will have the feel of an online travel site where individuals and families can compare different private insurance plans.