You will be expected to show your film and the best way to advertise your film is to create a movie poster.
Step one is to look up movie posters that you like. Collect them and make notes about what you like about them. Which fonts do you like? You should be creating your own fonts if you want to pass the design standard.
Take your own images of your cast to get the right images.
Come up with several posters and then get some feedback before you go with a final design which you will then produce to advertise your movie.
Here are some videos to help you design your cover.
I like Phlearn as they have step by step guides.
Keep in mind the 7 elements that all great movie posters must have.
If you want to explore more of the movie poster industry here is a good video looking at the colour schemes of posters.