Once logged into your account and creating a Campaing (or Community Project), you are given the possibility of adding a pitch video. 

Located on the second step of creating your project, go under Campaign (or Community Project) Description. There you can "Add video link" or "Upload own video", depending on your preference.

On the third step of creating your project, you can add multiple videos and multiple images, in the "Video Gallery - add more " and "Image Gallery - add more" sections.

Do not forget to save every time you add some content.