1. Processor cycle is a time to execute an elementary machine instruction. Note that complex machine instructions may need many cycles to complete.
2. The execution time of a program depends not only on the processor frequency but may also depend on many other factors like main memory speed, I/O speed, etc.
3. Processor frequency is the number of processor cycles per second. One cycle per second is 1 Hz. That means your 3GHz CPU runs 3.000.000.000 cycles per second.
4. Given that processor cycle is machine cycle, MCPS (machine cycles per second) equals the processor frequency.
I hope my explanations can help you. You can also consult with Wikipedia (http://en.wikipedia.org/wiki/CPU_cycle , http://en.wikipedia.org/wiki/Clock_cycle) or a good book on computer architecture (like the one from Hennessy&Patterson "Computer Architecture: A Quantitative Approach").