If you are starting sound therapy with tuning forks I recommend starting with more than one. The reason is because health, meditation, stress and pain relief etc. come much more easily and quickly with harmonics.
What is a harmonic? Most of the definitions I've found for harmonics are a bit scientific or assume a musical background. Here's one I pulled off a search:
A harmonic is an overtone accompanying a fundamental tone...
In sound therapy terms, your fundamental is the note you are playing so if you are using a 256hz tuning fork, 256Hz is your fundamental. Tap a tuning fork and listen away from your ears. You may here several tones, the actual note of the tuning fork and the overtones / harmonics which are the additional frequencies coming from the tuning fork. Bring the tuning fork to your ear to hear the fundamental more clearly. You should hear one dominant tone, the frequency of the fork or fundamental. All the other more subtle notes are the overtones or harmonics. You'll hear the same for most other instruments for sound therapy.
By playing more than one tuning fork you allow the harmonics from each play to off each other. It is harmonics which help to bring you to a still point, that moment of inner silence when healing and awareness take place.
One of the best ways I know to experiment and experience harmonics are with the Solar Harmonic tuning forks. Anyone who has had a session with the Solar Harmonics will understand what a still point is.
Can You Know What The Frequency Of Each Harmonic Is?
Harmonics can be calculated mathematically. Visit this site and enter 8Hz as the fundamental (8Hz is roughly the Schumann resonance or an earth frequency). Notice anything interesting about the 5th, 7th and 15th overtone/harmonic? Those are the frequencies of the Otto tuners. The Otto tuners are based on the harmonics of the Earth.
The Otto weighted tuning forks also create harmonics but because of the weight on each prong, the harmonics are hard to hear but that should not stop you. Since a harmonic is really a wave or vibration, place two weighted tuning forks on the body to send a harmonic wave through the body.