Lord of the rings Question: please answer!Whatdoes this mean:One Ring to.......

"One Ring to rule them all, One Ring to find them, One Ring to bring them all and in the darkness bind them"
Did any one understand what does this mean?
What does it mean?
please explain, as i'm not sure if it does mean that the ring will find them and put them under his control. But how can he find them, or put them under his control?
And why do anyone who see the ring have a tentation to steal it?
Please answer me!
and tell me if this description that i've found on a website is true (it took me hours to copy it!):

"In ancient times the Rings of Power were crafted by the Elven-smiths, and Sauron, the Dark Lord, forged the One Ring, filling it with his own power so that he could rule all others. But the One Ring was taken from him, and though he sought it throughout Middle-earth, it remained lost to him. After many ages it fell by chance into the hands of the hobbit Bilbo Baggins.
From Sauron's fastness in the Dark Tower of Mordor, his power spread far and wide. Sauron gathered all the Great Rings to him, but always he searched for the One Ring that would complete his dominion."

And at last, does anyone know a website where you can print a BIG map of the middle earth, to put it as a poster or something?
Thank you very much!:)