This is a good place to look for CPU specs: CPU-World
You need to find the specific CPU type looking at the CPU's manual or on the CPU itself
(Before connecting the CPU fan).
For example, check this picture of CPU from Wikipedia:
You can see this CPU's spec here: CPU-World - Intel i7 - 2600k 3.40GHZ
Just search for the model in the site.
If you want to compare performance of different CPUs, try Tom's hardware, they are the best at comparisons and reviews.
EDIT:
I thought you wanted to know where to see and compare the specifications of different CPUs, If you want to learn details about what each specification means, you can check this out:
Hardware-Revolution - 12 CPU Specifications Explained in Plain English
You are welcome to ask for more details if you want.
1I think that due to "... and compare" part this question is not a duplicate. E.g. which CPU is faster: one with a higher GHz or one with a bigger cache, etc. – haimg – 2012-05-28T22:03:26.103
@Tom I would agree with haimg that this is not a dupe. This is more about understanding the specs rather than just finding them. – BloodPhilia – 2012-05-28T22:36:38.713
@haimg: Comparison is trivial once you understand them, and that's what the other question already helps you doing. The other question does help you understand the specs (and isn't about finding them). – Tamara Wijsman – 2012-05-28T22:48:17.817
(cc @BloodPhilia) – Tamara Wijsman – 2012-05-28T22:48:29.533