someone please explain in a nut shell about ram

SInce i havent been reading up on pc's since my celoron 300a o/c years ago please explain.

How do i figure this ram thing out? i keep reading about
2100 2700 800mhz 333? 533? what is the difference and how do u figure out what is what? pc ram 1030? what is this stuff?

Read the thread directly above this one.