Für Elise is a bagatelle Beethoven wrote around 1810. Its opening alternates two notes a semitone apart, so the melody is easy to follow even if you have never played the piano. That opening is what falls onto the keyboard here.
Press each note the moment it reaches the keyboard. Tap the keys on screen, or press the letter written on the note if you are on a computer. Three speeds are available, and watching the example first makes the shape of the melody much easier to follow.
The melody uses black keys as well as white ones. If the notes come too fast, choose the slow speed and watch the example first. Once the shape of the melody is in your ear, the same notes are much easier to catch.