Hz was much easier to comprehend under the original name for the measurment, cycles per second. An A-440 tuning fork vibrates 440 cycles every second. As the number of vibrations go up, the pitch goes up, and it follows a mathematical formula. Every time the frequency doubles, the pitch goes up an octave. A standard tuning fork is 440 Hz, that's the fifth fret of the first string on a standard-tuned guitar. One octave lower is 220 Hz, which is the 2nd fret/3rd string of a guitar in standard tuning, or the 14th fret/1st string of a standard tuned 4-string bass. Another octave lower is 110 Hz, the A at the second fret of a bass. One more octave and you're at 55 Hz, the open A string on the bass.
Now the other aspect is that what we hear is mostly the overtones, not the fundamental. That open A string that's vibrating at 55 Hz also has nodes of it that vibrate at other frequencies. The ratio of those frequencies compared to the fundamental 55Hz tone is what gives different strings their character. The amount, nature, and exact mixture of overtones is why a flatwound string sounds so different from a roundwound. Those parameters are also why MY Precision sounds different from other Precisions (and a big reason why lots of bassist LIKE tweeters, despite the sanctimonious assertions of those who think an electric bass' sound is soley based on the fundamentals- If they only heard the fundamental of their strings, they'd probably hate the sound).
For the OP, it's simple physics. If you're still in school, wake up and pay attention in physical science when they talk about vibrations and waves. It'll help you a LOT with understanding how basses, amps, and speaker cabinets work.
John