How do the Dead Sea Scrolls impact modern apologetics? I understand that the 1946 discovery of almost a thousand ancient texts in caves on the West Bank has had a significant impact, I'm just trying to figure out what specific changes the discovery has had for apologetics. What do the Scrolls tell us about biblical authentication?

As someone who wants to be competent in apologetics, what should I know about the Dead Sea Scrolls?
From what I recall, the major impact of the Dead Sea Scrolls is that it validated the accuracy of the Hebrew Old Testament scriptures.  Prior to the discovery of the Dead Sea Scrolls, the earliest Hebrew manuscripts of the Old Testament were dated around 920 A.D.  The Dead Sea Scrolls date back to around 100 B.C.  

With this gap of about a thousand years, some supposed there would be massive changes uncovered.  This was not true, however, as the variances were of no significance.

There have been opponents of Christianity that made allegations that Christians had perverted the Old Testament text, introducing and rewriting prophecies to make it appear that there were Messianic prophecies which Jesus fulfilled.  Prior to the discover of the Dead Sea Scrolls, Christians had a difficult time proving that this did not happen, even though the reality of such an undertaking would have been rejected by Jewish people everywhere and would likely be recorded in history.

Thus, the major significance of the Dead Sea Scrolls is that it verifies the stability of the Hebrew Old Testament manuscripts from well before the birth of Jesus and Christianity, and on through modern times.  We can be confident that the Old Testament we read today has been accurately transmitted throughout history from at least a hundred years before the birth of Jesus.  

The prophecies of the Messiah that so accurately and specifically point to the time of Jesus and to the specific events in His life were not introduced after the birth of the church, but were there all along.