What's the Difference Between Network and Out of Network?

A family of four will probably have a deductable somewhere between 4 and 8 thousand dollars, that's in network. If you go to the hospital and they have a out of network er, then you're paying. That doesn't count forger deductable. You cound be unconscious going into the e r. You have no idea if the doctor working on you is in network or out of network. And the impact on you is thousands, could be tens of thousands of dollars. How did i get this complex?