Just about every keyboard nowadays comes with a MIDI interface. What can you do with it? Well, there are two reasons for a keyboard to connect to a computer.
1. You can record your own song and save it as a MIDI file or as a wave file. You can also import multiple tracks and gradually build up an entire orchestra.
2. You can drive through this connection a MIDI synthesizer software and thus expand its vast sonic possibilities.
Through a MIDI connection no music is transferred, but so-called MIDI commands. Note-On for example, means that a note should be played with a certain pitch and volume. On note-off, the sound is switched off again. About Change Program, the sound changed, etc. So that the computer can do with these commands something, he needs a program that converts these commands into sound. A synthesizer or sequencer.
The "Keyboard Synthesizer" is such a program. It contains 16 oscillators, which can build up an infinite number of combinations of sounds. He also has 3 LFO modulators, 16 envelope generators and 8 virtual effects processors. It can be played by a MIDI keyboard or by MIFI files. MIDI files are electronical notesheets, which are available for nearly all music pieces ever has been written. Just google "free midi files".