The term preferred by medical professionals is Emergency Dept (or ED), but most people say Emergency Room (ER), and I am most people.
First, this is not just a handy place to go where you can get tests done in the same place and then get advanced treatment if you need it. Often, people who go to the ER are disdained as drunks or freeloading illegals--yet doctors SEND their patients there. Urgent care centers send patients there. Some ERs have urgent care centers.Yes, they have to treat you regardless of ability to pay--but this is somewhat limited if you have no insurance..
If it's a weekend (which we call the Black Hole) or at night or if pain is horrible, we go to the ER. Most people there have insurance--ERs count on those with insurance to pay much of the freight.
ERs are infamous for their wait times. We have waited up to 13 hours with our elderly mother--during that time, they won't let you have water or food sometimes, it's problematical. Now, hospitals have put in check-in technology--sort of like an appt. You can even get phone apps for this. This way, even though it's an emergency, you can wait at home until closer to your appt. This is a problem, though, because chest pain really needs to be evaluated fast.
When you go, bring a list of your meds. Write it down now and put it in your wallet. You could even create a "go" folder--meds, doctor, people to contact, allergies, past medical history. Some people put a note on the fridge for paramedics to find the folder. I have never seen a paramedic check.
Try to get someone to go with you. This is especially important if you are old. Sorry to say, older people get shunted aside in ERs--I have seen it happen a dozen times.
Three other hints--leave the curtains or door open--this keeps you in the mind of the staff. And, two, if you have a choice, go at shift change--7 AM is good.
Three, if you are on Medicare and are kept in the ER for "observation," be sure you are admitted and not in some limbo status. If you are not admitted--the bills will tumble in like mad.
Bills come in anyway--some docs in the ER may not be on your plan. The hospital may not even be on your plan. It's a crapshoot.
So make sure the ER is your last resort, not your first.