Before starting to play, you have to manually create the folder where you want to save the Dreamcast BIOS. In fact, you have to download the BIOS separately and save it to your Android device's memory. Only then will you be able to use the emulator.
Reicast Dreamcast Emulator doesn't have any configuration options at all. You just have to add the image of the game to any folder on your Android device and select it. The file will execute in seconds and you can start playing.
Reicast Dreamcast Emulator is a superb Dreamcast emulator that works wonderfully. As might be expected, it hasn't been tried with all of the games in the Dreamcast catalog, but it worked with almost all of the games tested.