The goal is to connect bubbles that agree until you get to the “END” bubble.
The beginning bubble is circled in red.
It is connected to three other bubbles (blinking in the picture below).
Which of the blinking bubbles matches the starting bubble?

Puzzle2
 
The starting bubble notes are “C-D-E” going up.
The bottom left bubble has the “A-G-F” keys marked with arrows pointing down the keyboard.

Puzzle3

There is no match.
The second blinking bubble has the word “DOWN” in it.

Puzzle4

The notes in the starting bubble go up; the second choice says “DOWN” – no match.
The 3rd choice:

Puzzle5

The starting bubble notes – “C-D-E” going UP
The 3rd choice – C-D-E marked on the keyboard, with arrows going up.
It’s a match!

So, Draw a line connecting the two:

Puzzle6

Now, from the new bubble, compare to the surrounding bubbles, choose the bubble that “agrees” with it.
And so on, until you get to the “END.”

Puzzle7