Centers for Disease Control and Prevention (CDC): A part of HHS that monitors public health & spread of diseases - it's like a diagnostic tool used by doctors to identify what's making you sick.
Food and Drug Administration (FDA): Another agency under HHS; they regulate food safety, pharmaceutical drugs, medical devices etc. - think about them as quality control in a restaurant ensuring everything served is safe to eat.
Medicare & Medicaid Services: These are programs run by HHS providing health insurance for elderly & low-income individuals respectively - they're like financial aid at school helping students who can't afford tuition.