How do I make an essay about a movie called The Princess Bride??

We can't help with essay writing on this short answer space but I can give you some suggestions. You need to pick a theme or argument first. If you pick the theme of love, then include that in your initial argument or thesis statement. Example:

In Rob Reiner's famous film Princess Bride (1987), the theme of love is prevalent throughout the narrative.

Then pick two or three ideas about the theme of love and develop them.