how does health/medical insurance work?

i am 21 and am covered by my moms health plan, she works at hospital, if get a job somewhere else, that offers health insurance, do i have to get it? could i have 2 health insurances? if i dont get it, will i still be covered by my moms coverage?
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Yes, you can have two insurances, but one will be primary, and the other secondary. It is unusual for an insurer to continue to cover you at the age of 21 unless you are a full time student, though, so your Mom needs to check on that. If you are still eligible for both, all claims will go to the primary insurance first, and they'll pay whatever they pay (usually 80% after the deductible, but each plan is different). If the primary plan says you still owe money, then the claim is submitted to the secondary plan, which may or may not cover the additional expenses. It's up to the individual plan. Here's an example of how it might work: You are charged $1000 for a procedure. Primary insurance writes of $500 of it (nobody gets that, it's just gone), and pays 80% of the $500 that's left ($400) leaving you with $100 to pay. The secondary insurance also pays 80% ($80), leaving you with $20 to pay out of your pocket. If you have more than one insurance, be prepared for extra paperwork, though, because each insurance will try to get the other to pay. That's called Coordination of Benefits and delays the whole process.
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