"So today's lesson is...you kill each other off until there's only one left. Nothing's against the rules!"
Here, Kitano addresses the students, telling them what is about to happen. As Kitano is the children's former teacher, he uses the imagery of teaching ("today's lesson") to attempt dark humor. He explains the rules of the game, saying that it is essentially a fight to the death. Here, we see that he is a psychopathic and deranged character.
"Each weapon is different. Not just guns or knives either! It is random so maybe you will get lucky, maybe not. It eliminates natural advantages."
The children are shown a training video to explain what will happen during the game. The video explains that the children will each get a random weapon, which could be something advantageous or not. This is apparently to account for "natural advantages" like strength or height.
"There's a way out of this game. Kill yourselves together, here, now. If you can't do that, then don't trust anyone... just run."
This is something Shogo says to other students, telling them that if they want to get out of the game they should kill themselves. He then offers advice if they don't want to do that, saying to not trust anyone and run. Overall, this quote gives a fatalistic account of the game and the idea that it is almost impossible to get out alive.
