Parashat Devarim is the first Parsha in the Book of Devorim the 5th and final Chumash of the he Torah.
Moshe spoke word of rebuke to the entire Jewish Nation on that side of the Jordan in the desert, in the plain opposite the Red Sea, between Paran and Tofel and Lavan and Hazerot and Di Zahav. He did not openly rebuke them, out of respect for the Nation, but did so by alluding to the various incidents where they angered Hashem by mentioning the names of the places where they took place.
This rebuke was given in front of the entire Jewish Nation, so no one absent could later claim that had they been their they could have responded with defensive answers. Moshe therefore told them, since they were all there, anyone who had an answer, let him answer. 
Moshe had mentioned the desert although they had already left it and were now in Arvos Moav, alluding to how they had angered Hashem in the desert during the 'Incident of the Complainers' where they had demanded meat saying it was preferable to have died in the Hands of Hashem in Egypt where they had meat.