First, add all the words of your song, split up.
Then, replace the scripts in the “Song” section.

when I receive [Song]

Usually the message will have the name of the song you chose. Add a new message for every new song.
Next, for key mapping: There will be a variable (button) it will switch a sprite to that costume. Then, you just have to do

repeat until <key (button) pressed?>
change [time] by (1)
wait (0.5) secs
end

Then, another thing will check if the button was pressed in time. That part is not required to be changed.
For more help, reply to this message.
https://scratch.mit.edu/projects/1223356525/ - engine

guides aren't allowed in the forums, you might want to put this in a project instead

ametrine_ wrote:

guides aren't allowed in the forums, you might want to put this in a project instead

Ok, well the project is unposted so this is pretty useless