When you set it up for caching, the Slacker app will install a small sync program on your phone's memory card (i.e. the microSD card). Then, when you plug your BB in to your computer, the program will run automatically (or, with certain settings, you have to run it explicitly).
That is, the Slacker program will only cache when you connect your BB with a computer that has internet access.
When it runs, it will download and cache songs for the stations you have set to cache. The number of songs depends on your settings and the amount of memory available on your phone's memory card -- should be somewhere around 100 songs per station.
When a station is cached, and you go to play that station on your phone, it will play from the cache rather than using your data connection to stream.
