Using the word "enormous" to describe Mexico's capital city doesn't come close to doing it justice - so any generalization you may hear about the city should be considered with that in mind. In any city of this size, there are bound to be places where those generalizations fit, and where they don't. Mexico City deserves to be explored before you can really attempt to understand it.
The official name for Mexico City is Distrito Federal, and you may hear it referred to by the initials DF. Most visitors will concentrate their time in and around the historic centre, or Centro Historico, so the sheer sprawl of the entire DF shouldn't be much of a concern. You may want to research the locations of attractions you wish to see most before choosing a hostel in Mexico City then you won't spend all your time in transit between your hotel and where you want to explore.
No matter where you choose to stay in Mexico City, it's a good idea to be aware of public transportation options. There are several methods to choose from, including an intricate subway system and two kinds of buses, so there’s no need for expensive taxis. Of course, in a few areas, walking is one of the best activities - the scenery is in the architecture, the public squares, and the parks.
There are more museums in Mexico City than in any other city on earth, so there's sure to be something to suit every interest - even if you don't fancy yourself a museum-goer. Additionally, there are regular sporting events (car and horse races, as well as soccer games), a huge Six Flags amusement park just outside the city, ample opportunities for shopping in traditional markets, and an incredible variety of cuisine to try.