if we ignore the control lines, you`ll see a ram chip has address and data lines, the Data lines in a 1 byte wide chip has 8 lines and can represent any number from 0 to 255.
the address lines are like little storage boxes, and each box you can put in any number between 0 and 255 (data), a bit like the old pigeon holes or the way mail used to be sorted, one box for all the letters going to an address.
to 2^64 is is simple too, take the number 2 and then double it, you get 4, double that you get 8, 16, 32, 64, 128 etc...
in your chip, you have to keep doubling it 64 times, that`s a Massive number!
think about it, a chess board has 64 squares, put a small piece of paper with any number between 0 and 255 writen on it, on square number 1, then 2 peices on sqr 2, 4 on sqr 3, 8 on 4, 16 on 5 etc...
by the time you get to sqr 64, you`ll be an old man, have used up several pens, and have a pile of paper probably bigger than the empire state building!