ST. LOUIS (AP) — The St. Louis Public Library auditorium was filled with a cross-section of city residents: college students, small-business owners, church volunteers, working parents, the unemployed, retirees and more.

What brought them together was a chance to learn more about a linchpin of the federal Affordable Care Act — the online health insurance marketplaces that will give the uninsured a chance to purchase coverage in the months leading up to 2014, when those without insurance under President Barack Obama's new health care plan face financial penalties.

At the library, the policy expert from the Missouri Foundation for Health explained the labyrinthine federal program, outlining the four broad coverage plans (platinum, gold, silver and bronze) and eligibility standards. What she couldn't yet provide — three weeks before enrollment opens on Oct. 1 — were the most important details on premium costs and coverage levels.