If you want to learn what the specs mean, let's start by breaking down all the components as a starting point:
Intel® are the manufacturer.
Core™ i7 is the family of chips, it is the highest of Intel's current families (i3, i5, i7)
640M is the exact chip model.
2.8~3.46GHz is the chip's standard, and "boosted", frequencies.
35W is the chip's TDP (Thermal design power - the amount of power the cooling system in your computer should be capable of dissipating).
4MB Cache - This is the amount of L3 cache the chip has.
2 Cores - the number of physical cores that make up the processor.
4 Threads - using hyper threading, this is the number of virtual cores that your OS can use (each physical core is hyper threaded in to two virtual ones).
2.5 GT/s - is the maximum data transfer rate of the chip.