"Nothing rests; everything moves; everything vibrates." -- The Kybalion
"Energy is consciousness and it either contracts or expands to maintain or increase its rate of frequency. The process of how fast or slow energy contracts back towards its center point of source field, is the vibration rate. The process of how fast or slow energy contracts back towards its center point of source field, is the vibration rate. The process of how slow or fast that same energy expands away from the center point of the source field is the oscillation rate. The combination of both the pattern of vibration (contraction of energy) and oscillation (expansion of energy) speed is what determines the frequency rate of all energy and things. As our personal, collective and planetary consciousness raises frequency, the matter world, including our physical bodies, also becomes less dense as our frequency increases." -- Ascension Glossary
Just like electronics, we have electromagnetic fields. If there are two electromagnetic fields working together then they are in harmony, or resonance, with each other. Laws of physics maintain that sound-- when at the right frequency and amplification- can shatter glass. Why is this? Because all things posses a natural frequency/vibration level. So, as long as the sound matches the frequency of the magnetic field surrounding the glass, the glass will vibrate/break. No matter how loud the sound, if it doesn't match the resonant frequency of the glass, the glass will merely reflect the energy and as a result, it won't vibrate/break.
As with the example above, life works in a parallel fashion. When you think/feel something, you vibrate to it and thus, create a frequency. This same frequency essentially reaches out into the energy field of the universe and pulls to you the corresponding energy (persons, objects, and/or situations) that vibrate at that same frequency. Positive thoughts & emotions have a high vibration, hence, why they feel "light" and freeing; negative thoughts & emotions have a low vibration, hence, why they feel "heavy" and suffocating. You "vibrate" to something by being in the corresponding mental/emotional space of having already attained it. You control what you attract via your thoughts and feelings; this is where the law of attraction comes into play as both the law of vibration and the law of attraction are inseparably intertwined. When you practice one law --which we always are, for better or worse-- you're simultaneously practicing the other.
Recap: Spiritual Alchemy Tip#3: Law of Vibration -- "...Everything moves, everything vibrates.."
The electromagnetic waves that your heart and brain produce via your thoughts and feelings vibrate/resonate/attract to you the exact people, situations and things that match your personal vibration level, or frequency.