Hi there,
I was also sutcked in this part. I play on iPad.
It is a little bit difficult, I "discovered" that you need to press on one of these "planets" or colored rounds.
At a moment there will be be a little sound and thats ok.
When you hear this little sound keep pressing and move your finger to the middle of the screen.
That's it..
You need to do the same with all others
Hope this helps