Hz is the physical unit of frequency. It is pronounced "hertz".
1Hz means one oscillation per second. For example, if a pendulum swings once a second, its frequency is said to be 1 Hz. If it swings 100 times a second, then it is 100 Hz.
But Hz is a unit used in electronic science, and the analogy is just for the sake of understanding.
The same is true for the CPU, but it represents the frequency of oscillation of the electrons.
2.4GHz means that, in this processor, the electronic clock oscillates 240,000,000 times per second.
This represents the main frequency of the processor. This figure indicates "one way" of showing the performance of the cpu. It does not compare the performance of all CPUs.
For example, let's say cpuA, frequency is 1GHz. and cpuB, frequency is 2GHz. does this mean that cpuA is not as good as cpuB?
Not necessarily. Because, if cpuA has a frequency of only 1Ghz, it is able to process 3 data per oscillation (that is, per Hz).
While cpuB has a frequency of 2GHz, it can only process 1 data per oscillation.
So which one is stronger? Surely the lower frequency cpuA is stronger instead.
So cpu frequency can only be compared among cpu's of similar design. Comparing frequencies of cpu's of different designs doesn't compare performance. For example, the P4 can only be compared to the P4.
Cool Raid 2 can only compare frequency with Cool Raid 2. If you compare their frequencies directly to compare performance, you will get the wrong result.
There are many factors that affect cpu performance, and for the uninitiated there is no way to tell.
In fact, you remember one truth. You get what you pay for.
Cpu's with similar prices have similar performance.
So it's best for amateurs to buy cpu's from the price to compare.