If you plan to change your PC or to
replace your CPU, this information is pretty useful to have.
Online benchmarks
The best shortcut to compare two CPUs is to consult online benchmarks (by typing benchmark cpu on Google for example). You will find intensive lists of CPUs classified by speed, so you'll soon see the difference.
Model, frequency and cores
Without benchmark, one can also compare the frequency in gigahertz (ghz). The CPU that has the highest frequency is the faster one. The model is also very important, since a Celeron 3.0ghz is far slower than a Pentium 3.0ghz, you can look which one of two models is the most expensive to have a good idea of which one is the better. Finally, number of cores is also very important because if you own a dual core 2.0ghz CPU, you have twice 2.0 ghz at your service!