You need to have a brief summary of the overall background of the paper first, which will be used in the first demonstration.
Then, you should thoroughly understand the relevant content of your article in order to deal with the places where the teacher may make things difficult for you.
If your defense is not very stylized, you may also get some information by asking the teacher directly, such as his opinion on this paper, the theory he wants you to choose, and then guess what he wants to ask you.
It's not difficult. Don't be nervous. Pay attention to the organization of words.
Let's go