MuseScore comes with a special type of file called a SoundFont that tells MuseScore how to play each instrument sound. Some SoundFonts are custom designed for classical music others for jazz or pop, others are large and take up a lot of memory, still others are very small and light-weight. The latest versions of MuseScore (version 0.9.6 or higher) come with a relatively light-weight, general-purpose SoundFont called, "TimGM6mb.sf2".