My computer has a CPU with 4 cores and 4GB RAM.
What I want is to find out, if I am using all the available power that my PC offers to me? How can I do this?
Well, I do believe - actually - you're using not just your PC at its full potential, you're also wasting it!
The problem is (or at least may be), you don't want to use all the powerhorses all the time! Electricity costs.
If you do care about this point, install cpufrequtils and this http://www.webupd8.org/2011/07/cpu-frequency-scaling-indicator-fixed.html.
Otherwise, you're good to go!