As a member of an HMO ("Health Maintenance Organizations"), you'll be required to choose a primary care physician (PCP). Your PCP will take care of most of your health care needs. Before you can see a specialist, you'll need to obtain a referral from your PCP.
With an HMO you'll likely have coverage for a broader range of preventive healthcare services than through any other type of health insurance plan. Additionally, you probably won't have a deductible to pay before services are covered. You also won't have to worry about much if any of the paperwork involved in submitting claims.
However, keep in mind that you'll likely have no coverage whatsoever for services rendered by non-network providers or services rendered without a proper referral from your PCP.