It is the dream of any musician wannabe lacking their desired instrument
Most patents are boring, but there are some that describe interesting things. Otherwise there wouldn't be any fun gadgets and computers.Samsung is the one that got granted a fun patent not long ago, though some may say it isn't all it's cracked up to be.
Matters of opinion aside, the patent describes a portable music player that also allows owners to play along a tune.
Pressing keys would add sounds or modify the music. The concept is not so different from plucking the cords of a guitar, or manipulating an electronic keyboard.
A motion detector, according to Samsung, detects the fingers on the other hand and interprets what effects they would have if they were actually interacting with the instrument in the song.
Samsung may or may not build one of these things. It all depends on consumer interest really.