* The original recording: This is the version from the Disney Channel movie. You can't "get" the score in the sense of obtaining its musical arrangement; it's a copyrighted recording.
* Sheet music arrangements: Various arrangements of "Breaking Free" for different instruments and voice parts (solo, duet, choir) are available for purchase from online retailers like Sheet Music Plus, Musicnotes.com, and others. These will provide the notes, rhythms, and chords needed to play the song.
* Karaoke versions: These remove the vocals, allowing you to sing along. You can't get the original score from these, but they are a way to experience the song's melody and accompaniment.
* Transcriptions: Someone might have created a transcription (an amateur attempt to write out the score based on listening to the recording), but these are usually not professionally published and may not be completely accurate. You might find them on music forums or websites dedicated to fan-made arrangements.
In short, to get a playable score, you need to purchase a legally licensed sheet music arrangement from a reputable online music retailer or music store. Searching for "High School Musical Breaking Free sheet music" will yield numerous results.