Mr. Frank says this line when they are all fighting.
He is saying that they don't need the Nazis to destroy them. They are destroying themselves by fighting. In this scene, they were fighting over food, which was certainly important -- however, Mr. Frank is saying that the good of all must be considered before individual needs.
Mr. Frank is saying that in order to survive, some sacrifice must be made, and the fighting must be stopped.
Answer:
one: know what the whole project is about i.e that's know if it's educational,talking business contemporary issues etc
two: check for topics in the internet.
three : when that's done, you check on recent videos on the topic