In transport services, you take on the task of providing transport for goods or passengers among contracted cities. Cities reveal as you play, which brings new needs for passengers. As you care for your passengers your cities grow and produce more passengers and there is a lot of waiting passengers, you will have to pay back some tickets and your city might lose its shine as people do not want to live in a city cut off to civilization. Also once your city reaches a bigger size, you will build a factory producing resources, which you can distribute into your other cities to make a profit.
You will be able to build roads for buses and trucks, as the cheapest variant for the short distances. Rails for trains to travel longer routes with huge capacities or airfields with planes for very picky passengers, that are designed for an even longer distance of travel.