By Monifa Thomas @MonifaThomas1

By now, you’ve probably heard that something big happens Tuesday with the Affordable Care Act, informally known as Obamacare. But you may not know exactly what is going onthat is. Don’t feel bad. A lot of Americans are in the same boat. Here’s what you need to know:

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THE UNINSURED AND MEDICAID:

Illinois was one of 26 states that decided to expand Medicaid, the state and federal program for low-income people. Newly eligible Medicaid enrollees must be between 19 and 64, make less than roughly $15,860 for an individual and must have been a legal immigrant for at least 5 years or be a U.S. citizen. Illinois law was changed to expand who could qualify for Medicaid, but you still must apply for it. If you visit the Illinois Health Insurance Marketplace website after Tuesday, you will be guided through questions that determine if you need Medicaid or private insurance. Then you will be directed to the Illinois Medicaid website, if you qualify. You can apply for Medicaid anytime after Tuesday.

THE ONLINE MARKETPLACE:

The Illinois Health Insurance Marketplace is supposed to provide a one-stop shop of affordable health options for those who lack health insurance or are looking for cheaper options if they’re self-employed. We’re still waiting to see if the health insurance prices live up to the hype, but the examples recently shared by Gov. Pat Quinn gave suggest they it will. Individuals and families with income between 133 percent and 400 percent of the federal poverty level are supposed to receive subsidies on a sliding scale if they get insurance through the marketplace.THOSE WHO DON’T BUY INSURANCE:

THOSE WHO WILL STAY UNINSURED:

The federal health care overhaul is expected to provide 31 million uninsured Americans with health coverage by 2019 — the largest expansion since Medicare was created. But about 26 million people will remain uninsured under health reform, the Congressional Budget Office estimates. About one-third, or 8 million, of those people will be undocumented immigrants, the agency says. Others who are exempt from having to buy health insurance are the incarcerated, people with religious objections, members of American Indian tribes and people for whom the cheapest available insurance plan would cost more than 8 percent of their income.

THOSE WHO ARE INSURED:

Some changes are coming for people who have employee-based insurance, but not on Tuesday. Beginning Jan. 1, insurance companies will no longer be able to deny enrollment for a plan if a person has a pre-existing condition, though Karen Pollitz from the Kaiser Family Foundation noted that most large employers stopped pre-existing exclusions after the Health Insurance Portability and Accountability Act (HIPAA) was enacted in 1996.