Let's say you are based in London City and want to have a second hub in Malaga. All you flights have to start at London, but you can fly 2-leg routes, for example London-Malaga-Algiers-Malaga-London. That way you can have lots of flights from Malaga as well as from London, just fly London-Malaga-Rome-Malaga-London, London-Malaga-Barcelona-Malaga-London, etc. The problem is that you will then have lots of seats on the London-Malaga route. You can circumvent this by making flights such as London-Frankfurt-Malaga-Frankfurt-London, London-Madrid-Malaga-Madrid-London, etc. That way you can still focus on Malaga but don't have to start all your Malaga-originating flights with the London-Malaga leg. Notice that the game considers these 2-leg flights as two separate flights. For example, with the London-Malaga-Algiers-Malaga-London routing you will transport passengers London-Malaga and back, and Malaga-Algiers and back, but not London-Algiers.