What do Katniss meant by let the 74th Hunger Games begin cato let them begin for real?

katniss meant that she was angry for rue's death and she will show cato in these game that she will win.

^This cannot be true, as Rue has not died at this point. She thinks this statement to herself as she sees Cato's outrage when their supplies are blown up from the mines/bombs which are reactivated by the D3 Male. Basically, they are called the Hunger Games as 'exposure can kill just as easily as a knife.' This means that as the Careers are used to being well fed, they are not used to foraging and do not know which plants are edible. Katniss then has the upper hand as the Careers have to either risk dying of poisonous food found in the arena, or starving to death. Therefore, she says it as she feels she has finally levelled the playing field, but she really now has the upper hand.