As for determining the rate of computations the processor can perform, there are many other variables that come into play. The clock frequency tells you how long it takes to execute one instruction. A simple action like add, subtract, or compare two numbers is generally considered to take one cycle. However it may take a certain processor multiple clock cycles to perform a single function like multiplication or division or two numbers. If you want to gain a lot of insight, take a course that deals with computational design (like low-level FPGA work), and or take a class in Assembly language. Both will give you good opportunities to see how long (how many steps) simple computational activities can take.
When you get into multi-core, multi-threading, look-ahead, pre-caching and predictive algorithms that current CPUs employ, it gets really, really ugly, really, really fast.