I'm about to fly with United internationally. What do I expect? I'm used to flying with southwest?

United isn't as clear about things like southwest. We're flying from Nashville to Chicago and we having at 4 hour layover. Then we're fly for 13 hours to Japan.

How much is 2 checked bags? SW is free.
Is this assigned seating or can webpick where we wanted sit? I'm going with 5 people and I want to be with them but worried that's not happening.
Do you we have free Wi-Fi or we have to pay?
Is there usb outlets on the plane? I'm getting a battery bank just in case.
Do they provide complementary snacks and drinks and we have to pay for them.

Any other advice or tips for this airline and long haul flights?

International flights generally include one or two checked bags. They usually have USB ports and semi-ok complementary Wi-Fi. If you want to site together, you are best off calling the airline and seeing if you can get seat assignments. There's always the chance you will have seat assignments and they will change them last minute, but your chances of sitting together are greatly increased by calling ahead.

Southwest does the "zone boarding". Some other airline are starting to do so, but unlike SW, they generally have assigned seating. My recommendation is to call now (expect to be on hold for a while), see about getting assigned seats together, and ask about bags. I've flown in-stop to Japan form Washington DC and it's a killer. I was fortunate to get a last minute upgrade for $200 that not only got me more leg room, I had no one in the two seats next to me so I could really stretch out. I wasn't so lucky on the way back, and 16 hours in an economy seat is no mas

Southwest is the only US airline that lets people sit anywhere. Every other airline has assigned seating. You should be able to pull up your reservation on United.com and pick seats.
Somewhere on their website is their baggage policy. International flights usually include a free bag or two.
Your reservation should say what type of aircraft you are on. You can look up what the plane has in terms of entertainment, USB ports, etc on seatguru.com (you can also just plug your flight info in there).
International fligths have free meals. Don't plan on anything free other than a cup of something to drink on your domestic leg. If they have any food on that flight, you will have to pay for it (unless you are in first class).
Don't expect Wi-Fi while flying over the Pacific. Expect to pay for it.

Very bad comparison. Southwest doesn't really fly international. Yes they fly to caribbean and mexico, but that is it.

Why don't you ask the person who booked/paid for all the tickets?

And yes you have to pay for Wi-Fi. As for USB ports, that all depends on what aircraft you are on and where you are seated.

Go to the United site online and put in your confirmation number. You can look at what seat you've been assigned, and choice among any empty, non-premium seats. You should have chosen a seat when you made the reservation.
You are probably going to be on a non-United flight. When I flew with them last time, I was able to get seats to Chicago and from Chicago to my first stop, but then not on the second flight because it was operated by Lufthansa. Lufthansa only lets you choose seats 24 hours before your flight. But the planes are better and food is better than on United. Go to seatguru.com and put in your flight number to see the amenities on the plane. They'll feed you a couple of times, but it won't be great food. I always take a packet of nuts.

BTW, if you're coming back through Chicago, it's awful right now. They're doing something to the train between terminals, so you have to go outside and wait for a bus. Then you have to go through the whole security thing again.

The United website will tell you the baggage allowance for your particular route. I believe that you are given 2 free checked bags on that route, although there are weight and size restrictions.

You have assigned seats on United. You can often choose your seats at booking, or anytime between booking and travel. Whoever booked the tickets should look into that.

Go to seatguru.com, plug in your flight information, and see which aircraft you are scheduled to be on. That will let you know if there are USB ports available. Be aware that your assigned aircraft can always change.

Wi-Fi is not free. Even when you pay for Wi-Fi, it usually does not support streaming services.

You do get free food - meals, not just snacks - on long-haul flights (Chicago to Japan). Beer and wine are also complimentary on that flight. You might get a small snack on your Nashville to Chicago flight.

You can use these links for additional information:

Other tips:
Bring plenty to keep you busy
Dress comfortably and in layers
Get up and walk around periodically

It is nothing like flying Southwest. Do you honestly think for a 13 hour flight they are only going to have snacks and drinks? It will be 2 meals usually dinner and breakfast. Have specific diet then you can request it in advance.

Seats are assigned, you go online and look to see what you is available. Then pick there or call the airline and have you put together.

You will get 2 checked bags for free, unless otherwise stated by the airline.

Novel idea CHECK THE WEBSITE!

Make sure you take toiletries and at least 1 change of clothes in your carry on. That way if your luggage is delayed you are okay

Look on United's web site.

United is a great airline you'll be fine