More than three years after President Obama signed the Patient Protection and Affordable Care Act of 2010, some of the big changes in the nation’s health-delivery system that the legislation mandated are about to go into effect. With the pro and anti forces already claiming victory, there’s a lot of misinformation going around about how the new system will operate. Critics who claimed that the reform, which ran to nearly two thousand pages, was too complicated even to get off the ground have been discredited. But big questions remain about how things will shake out.

The good news is that, in large parts of the country, there’s been substantial progress toward getting the system up and running. Last week, California, the most populous state in the country, rolled out details of its online health-insurance exchange, through which people and families without group coverage will be able to purchase individual plans.

Starting on October 1st, people will start enrolling in new plans through the exchanges, and come next January, all Americans (with a few exceptions) will be legally obliged to acquire some sort of health coverage or face a fine. Some low-income people who aren’t currently eligible will be able to enroll in Medicaid, the federal system for the poor and indigent. Other low-to-middle-income families will be able to obtain federal subsidies covering up to ninety per cent of their monthly insurance payments. Health insurers will be prohibited from denying coverage to individuals, or charging them higher rates, based on gender or preëxisting conditions.

The reform was designed to do two things that might seem, at first glance, contradictory: expand coverage to the estimated forty-five million Americans who are uninsured and hold down costs for everybody else, taxpayers included. When the bill passed, I expressed some skepticism about whether this would prove possible, but that was just speculation. Now, or pretty soon, we will have some actual evidence about how the system will work.

Several things bear watching:

1. How many insurance companies will offer coverage through the new exchanges?

Under the current system, two or three companies dominate the individual insurance market in many parts of the country, and competition is squelched. The theory behind Obamacare is that, with a system of exchanges, vigorous competition among numerous providers will drive improvements in the quality of health care and hold down costs.

On this score, the initial outlook is encouraging. In California, nearly three dozen insurance companies submitted bids to offer coverage on the state’s new exchange. Thirteen were selected, including some of the biggest participants in the current system, such as Kaiser Permanente, Health Net, and Blue Shield of California. Notably absent were several big national insurance companies—UnitedHealth, Aetna, and Cigna—but the fact that so many firms did choose to get involved was a plus.

The Obama Administration insists California is likely to prove the rule rather than the exception. According to an analysis that the White House put out on Thursday, “About 90% of target enrollees will have five or more difference [sic] insurance company choices.” The figure is based on data from nineteen states, which are home to about eighty per cent of the folks who are likely to use the exchanges.

2. How many of the uninsured will use the new exchanges?

Insurance works by pooling risks. If more healthy young people enroll, it will help bring down everybody else’s costs. But if plans turn out to be prohibitively expensive, many young people may initially choose to skip coverage and pay the fine, which starts out pretty low—ninety-five dollars for a single adult—and increases sharply in subsequent years to six hundred and ninety-five dollars in 2016. (The Kaiser Family Foundation has posted a helpful primer on the individual mandate. For those who want to know even more about how it will operate, the I.R.S., which will be in charge of tracking enrollment and collecting fines, has published an extensive Q. & A.)

Some preliminary cost figures from Covered California, the organization that will operate the state’s insurance exchange, illustrate the issue. The premiums will vary by age and geographic location, and also by the benefits and level of co-payments included in the plans, which come in four types: Bronze, Silver, Gold, and Platinum. Let’s take a forty-year-old single person with no dependents. For a typical Silver plan sold through the exchange, his or her monthly premium will be about two hundred and ninety-four dollars a month. According to the Los Angeles Times, the average premium last year for individual plans sold on eHealthInsurance in California was just a hundred and seventy-seven dollars. That’s an increase of about sixty-six per cent. “These rates are way below the worst-case gloom-and-doom scenarios we have heard,” Peter V. Lee, the executive director of Covered California said. “But let’s be clear, some consumers will have prices that go up. There may be some sticker shock.”

Two important points need making here. First, it’s not an apples-to-apples comparison. The higher premiums in the new plans reflect the fact that insurers will be mandated to provide more benefits than many current plans do. Second, thanks to generous federal subsidies, paid directly to insurance companies, many low-to-middle-income people will pay a lot less than the quoted price. Covered California says more than half of the people shopping on the new exchange will be eligible for subsidies. According to its estimates, a forty-year-old Angeleno who earns about twenty-three thousand dollars a year, twice the federal poverty level, would end up paying about ninety dollars a month, rather than more than three hundred dollars a month, for one of the lower-priced Silver plans.

Still, some existing purchasers of individual insurance who can’t be classified as rich, and who won’t be eligible for much if any help from the government, will end up facing sharply higher rates. Take, for example, a single forty-year-old Californian who makes forty-five thousand dollars a year, roughly four times the poverty level. He (or she) won’t be eligible for any subsidy, which means he (or she) will have to pay the entire cost, which is three thousand five hundred and twenty-eight dollars a year. It remains to be seen how this will impact enrollment rates.

3. To what extent will employers start to shed their health-insurance plans, or shift the costs of them onto their employees?

The Affordable Care Act requires all businesses with fifty employees or more to provide health coverage. However, some critics argue that this provision could backfire. Given that corporate insurance plans cost up to five thousand dollars a year per person, businesses, rather than complying with the reform, could have a financial incentive to pay a fine, which amounts to about two thousand dollars per employee.

Although this argument is usually made about small firms that don’t currently offer insurance coverage, it could also apply to big firms that do. As the individual exchanges get up and running, the skeptics say, many corporations will start to shed their corporate plans, leaving their workers to look after themselves. Douglas Holtz-Eakin, a former head of the Congressional Budget Office who advised John McCain in his Presidential run, says tens of millions of Americans could lose their employer-provided plans. Other estimates are more modest, but not inconsequential. Earlier this year, the C.B.O., which initially said about three million workers would lose their coverage, raised that figure to seven million.