In the Android App, it's possible to play the trailer for a movie when viewing that movie's details. You can also make use of the Cinema Trailers feature to have trailers played automatically before a movie to help recreate that real cinema experience.
Currently, only trailers are supported in the Android App; support for other extras will be added in the future.
Related Page: Plex Apps > Miscellaneous > Cinema Trailers & Extras
Quick Play Trailer
To play the trailer for a specific movie, click the Play Trailer button on the detail page of that movie.
In the standard mobile layout, the button is available in the inline toolbar.
For the TV layout, you can access the Play Trailer button in the left actionbar on the movie details screen.
To get the cinema experience by playing trailers before a film you must tell the App how many trailers to play before a movie.
The types of trailers chosen is determined by the settings in the Plex Media Server.
Related Page: Plex Media Server > Server Settings > Extras