You can find a pretty long description of the Two Minutes Hate in Chapter 1.
But pretty much what is going on is that all the people get together at some specified time and the vent their hatred at someone for two minutes. In the Two Minutes Hate that we see in this chapter, they are supposed to be angry at Goldstein (he's always in them) and at the rows and rows of Eurasian soldiers that they see marching on the screen.
Basically, the people just completely freak out. They get to the point where they are jumping up and down screaming at the screen and someone even throws a book at the screen. As the book says:
In its second minute the Hate rose to a frenzy. People were leaping up and down in their places and shouting at the tops of their voices in an effort to drown the maddening bleating voice that came from the screen.
The Two Minutes of Hate is a daily exercise where members of the Party are required to hysterically express their negative feelings towards enemies of the state, particularly towards Emmanuel Goldstein and whichever army Oceania is currently fighting. Members of the Party pack tightly into a room where images of Goldstein and the opposing army are displayed on a telescreen. The Party members begin to shout, cry, and viciously scream at the enemies on the screen as they work themeselves in a frenzy. The Two Minutes of Hate is the government's way of maintaining an atmosphere of hysteria throughout the Party and allowing its citizens an opportunity to vent their pent-up anger. Although Wilson is opposed to the entire exercise, he cannot help but join in. The frenzied atmosphere is contagious and he begins to scream along with the others.