How can Esperanto be used, once I know it?
You can:
Read novels | read poetry | translate works | go to local meetings | travel (Pasporta Servo) | start a blog | attend national and international congresses | publish a dictionary with specific words | do social networking (Facebook, Twitter etc) | give Esperanto lessons | listen to Esperanto music (online) | listen to Podcasts | write your autobiography in Esperanto | write poetry | research the history of the language | invent new words | read news |

But I can do these things also with other languages!
Yes of course. Esperanto is a normal living language. And you can do with it all the things that you can do with other languages. Only much sooner.