Jobs are the easiest way to earn money in the game. Jobs are usually Regular Cargo and Regular passengers, called Bitizens. If you build more airports farther away from each other, Jobs may have payment in Bux. The further the destination is, the more the bitizen/cargo will be paying. In global events, a job will appear with its name and destination in blue.
If you want to refresh jobs, scroll up all the way until you see a bar and let it progress through. Then it should ask for you to refresh for these amount of bux: 2 bux will refresh class 1 airports, 4 bux will refresh a class 2 airport, while 6 bux will refresh a class 3 airport. If refreshing an upgraded airport, each upgrade will increase the bux refreshment rate.