Below you have the Android App that I've created in AppInventor2. This has a lot of buttons. You can see the cahracter each button will send so then, later in the code each time you receive one of those characters, you could program the Arduino to do something. In my case I send "1" , "2", "3" and "4" for front, left, back and right arrows and I move the tank in these directions.
I've isntalled the App. I've uploaded the BT code to my Arduino and made the connections as in the Schematic. Enavle BT on your smartphone and connect to the HC-06 module. Enter the App and control the tank movement and sounds. Quite cool right?
For the DF player to work you need the DF player library taht I've used. Also, you need a micro SD card and a small speaker. On the empty SD card create a folder and name it mp3, this is important. Then inside the mp3 folder copy your mp3 files and give them names in this way: 0000, 0001, 0002 and so on. You could download my tank engine, fire and movement sounds from below in z zip file and copy that folder tou yuur SD card.
You have a tutorial on how to use the DF player module on this link. For more read that tutorial and make that example code. Make sure you install the library. I hope taht you liek this tutorial. Consider supporting me on my PATREON page. Thanks!