Hertz are a measure of frequency, simply phrased in a way that makes a little more sense for the average user. Hertz describes cycles per second. Megahertz (MHZ) is just hertz with the "mega" prefix indicating 1 million hertz, or 1 million cycles per second.
The energy of an EM wave can be calculated based on its equivalency with the speed of light; c will always equal the wavelength times the frequency. Thus a high-frequency wave will have short wavelengths, and vice versa.
To calculate the energy, we can use a separate equation, based on the Planck constant: E = hf, where h is the Planck constant and f is the frequency. This indicates that increasing frequency will correspond to increasing energy.
Thus, when comparing a frequency of 90,500,000 with a frequency of 107,100,000, 107.1 has a higher frequency and therefore a higher energy.
Doing the math, the energy of a single photon from either of these stations is still significantly less than anything you could feel or see, which explains why they can be passing by us without any apparent effect.