Big Oh Notation and Heaps

Hey guys. I have a mid-term next friday, and my teacher is giving me an exam from the AP Computer Science AB test. I asked her what would be on it, and i am comfortable with most of the topics (like Stacks, Queues, TreeSets, BinarySearchTrees, etc.), but I have been having trouble with a few topics.

Big Oh Notation. I understand what the point of it is, but i have no idea how to figure it out. For example, if the test gives me an algorithm and i have to figure out the Big Oh Notation, i have no idea how to do this.

Heaps. I understand what they are and why they are used, but i can't seem to understand their Tree representation.

Any help would be greatly appreciated. I am currently reading my textbook trying to understand each topic, but i'm not comprehending it =[