It's one of online slots which offer the bonus games on the additional screen. There are four scatter symbols on Jazz Time Slot. To trigger the Jazz Jam Session you must hit three grand pianos after spins anywhere on screen of basic game.
On second screen you will see four instruments. They are a double bass, a grand piano, a guitar, and a trumpet. To start game click on one of them. An instrument will play a tune in harmony with the bass line rift. You can pick up to 4 instruments until when one of the instrument plays out of tune. Then game will be finished.