How do Airlines make Money?

I don't get it. If your average jet costs $20 million each- or more- how do airlines make money? Even if all 100-300 seats sell for $200 each, that's still a considerable profit loss. And that's just for one jet. So how do Airlines make cash?

New Ulaanbaatar Airport is 49 minutes away from downtown Ulaanbaatar. How is that going to work?

At first I was wondering why they were building a new airport when they already had a perfectly good one but then I found out that expansion at the current airport (Chinggis Khaan International Airport) is impossible because of the mountains that surround it. So that makes sense but how is Ulaanbaatar going to manage having it's main international airport being a 49 minute drive (courtesy of Google Maps) from it's downtown area? How can a city's airport be so far away from the city?

Can you use only the return portion of a round trip plane ticket?

I have a trip booked in October and I need to change the day I leave from Sunday to Saturday. It is a basic fare so I can't make any changes. I think the least expensive work around is for me to buy another 1-way ticket leaving on Saturday, and using the return portion of my original ticket. Does anyone know if you can do this? I tried to call the airline but they are slammed with calls due to the incoming hurricane…