How did the Yalta and Potsdam Conferences contribute to tensions between the East and the West following WWII?

Yes

They didn't contribute to tensions themselves. Rather, they laid out the expectations and responsibilities of the various allied powers in the aftermath of the war, and the Soviet Union almost immediately began breaking those treaties and demonstrating that they would not be living up to those expectations.

I could give you MY lecture...but I am not always considered to be Politically Correct. You need to read your textbook to see what answers your teacher is going to accept. If he is your typical liberal (Marxist) I can pretty much guarantee he would not like MY answers, and would give you a failing grade.

During the Yalta and Potsdam conferences bets were taken by most of the delegates on the future progress of any "cold war" that would probably occur afterwards.