We use a background music in the demo but we are not allowed to redistribute it, so you need to do it manually yourself. You can find the download link in the Credits.pdf file located inside the Sounds folder. Once you have downloaded the music and imported it into your project (remember to set its Load Type as Streaming, which is the recommended setting for background music), you just need to drag it into the Audio Source component of the BackgroundMusic object located in the home scene.
How can I add a new level to the map?
The level map contains a scrollable list of buttons that are used to enter the levels (in the scene's hierarchy, you can find the list in Canvas/LevelMap/ScrollView. These buttons are instances of the LevelMapButton prefab, which has a Num Level property that indicates the level number:
You will need to have created the corresponding level with that number with the level editor.