The "historical present" or "narrative present" is very common in storytelling. In the case of a movie, we feel that we are watching the events on the screen as they happen. Even if it is an historical movie, we feel that the events are happening now. Therefore, it is common to use the "historical present." Here's an example--part of a synopsis of the plot of the famous movie, "Citizen Kane." It's 1941, and newspaper tycoon Charles Foster Kane (Orson Welles, who also directed and co-wrote the script) is dead. The opening shots show Xanadu, Kane's vast, elaborate, and now unkempt estate in Florida. Interspersed with segments of his newsreel obituary are scenes from his life and death. Most puzzling are his last moments: clutching a snowglobe, he mutters the word "rosebud." Kane, whose life was news and whose newspapers not only reported but formed public opinion, was central to his time, a larger-than-life figure. The newsreel editor feels that until they know who or what Rosebud is they won't have the whole story on Kane. He assigns a reporter called Thompson (William Alland) to investigate Rosebud. Thompson digs into Kane's life and hears a lot of stories, but none of them reveal the meaning of Rosebud. The reporter sees Susan Alexander Kane (Dorothy Comingore), the tycoon's ex-wife; she's drunk and won't speak to him. Then he reads the unpublished memoirs of Mr. Thatcher (George Coulouris), Kane's early financial adviser and childhood guardian, who later became a prime target of the Kane newspapers' trust-busting attacks. In one of many flashbacks, the Thatcher memoir shows Kane's mother signing guardianship of the boy and his fortune over to Thatcher, despite his father's objections. When Charles objected violently to being sent away with Thatcher, Kane Sr. remarked, "what the kid needs is a good thrashing."

You can use the same tenses you'd use to describe a real event. Just preface it by informing your listeners that it is all in a movie. Hope this helps, Lydia! :)

We primarily use the simple past to describe something that happenED (past tense) in a movie. However, it's common for native speakers to use the present tense (in the same way that news agencies do) because people are subconsciously apt to be more interested in a present moment than one in the past. It looks something like this: So then the man opens the door and sees a dinosaur running towards the house. He runs and hides in a cupboard, but the dinosaur finds him...

Both past and present tense are fine. But you need to keep your writing in the same tense when describe a real event.

English does not have a separate tense for fictional events, so you should use the same tenses that you would when describing real events.