If you have a txt file and the mp3 go to your UltraStar directory:
Open “Songs” and create a new directory in it. Example:
Now open (example: “Foo Fighters - My Hero) it and add the mp3 and the txt file.
It should look like this:
Now you just have to start the game and select your new song!
If you still have questions: visit our FORUM and ask!