This is a huge law and so any explanation of it will have to be an extreme simplification.
The basic idea behind this plan is that everyone will be required to have health insurance. Anyone who does not must pay a penalty. Insurance companies will be required to insure everyone, regardless of whether they have preexisting medical problems. The companies will have to charge even those people premiums that are similar to those charged to healthier people. Subsidies will be given to those who are relatively low income States will need to set up insurance "exchanges" where people who aren't insured by their employers can choose from a selection of insurance policies.
This is all supposed to ensure that everyone can get insurance and it is supposed to reduce costs as well.
Health care for colors.