Hi confuzcious,
I'll give it a shot. As onacruze said, you can get a flavor for some of the details in the link he gave.
As briefly as I can manage, secular history dates the fall of Babylon to the Medes and Persians under Cyrus to October, 539 B.C. The Bible states in that in Cyrus' 1st year, he issued an order allowing the Jews to return to Judah. The Jews could have been back in Judah by about September of either 538 or 537 B.C.; the Watchtower Society prefers the latter date. The Society interprets the "70 years of Jeremiah" (Jer. 25:11, 12: 29:10) inconsistently as both years of desolation of Judah and as years of the Jews' captivity in Babylon. Going back exactly 70 years from September, 537 B.C. gets you to 607 B.C. They claim that Jerusalem fell to Nebuchadnezzar at that time, and that its desolation began.
Unfortunately for the Society, its chronology is inconsistent with both the Bible and with secular chronology, so that when it claims it is using "Bible chronology" it is lying. It is using its own flawed notions. A good example of its ignoring what the Bible actually says is in its totally ignoring the unambiguous statement in 2 Chronicles 36:20 that the Jews would serve Babylon until the "royalty of Persia" began to reign. Obviously they served only until October, 539 B.C., because that's when "the royalty of Persia" overthrew the Babylonian kings. In view of the clear statements of Jeremiah 25:11, 12, which says that the Jews would serve Babylon for 70 years, and that when 70 years were fulfilled Babylon would be punished, and that punishment occurred in 539 B.C., it's again obvious that the 70 years ended in 539 B.C., and not in 537 B.C. as the Watchtower Society claims. Check the link onacruse gave for a lot more information.
This stuff is extremely important for ex-JWs to understand, in order to understand why JW leaders are not who they claim. If the 607 date is wrong, then so is 1914. If 1914 is wrong, then so is 1919. If 1919 is wrong, then JW leaders (the "anointed remnant") were not appointed "over all Christ's belongings" in 1919. But because they claim fulfillment of "Bible prophecy" upon them, and claim to "speak in Jehovah's name" and to teach truth in God's name and claim to be the true spiritual authorities over all mankind today, their claims are false. And because they teach falsehoods in God's name, they fit their own definition of "false prophets". And the dominoes keep toppling.
AlanF
