Ghost Vacuum

Tap on the ghost icon on the upper right corner of the screen. You'll notice the second icon in the dropdown is active now (not grey). That is the vacuum. Tap on it activate it.

With the vacuum activated, press a finger to your screen and hold. You should hear sucking sound and a whirlwind will appear under your finger. You can drag it around and when you bring it near a ghost, it'll get sucked in and pop and give you Goo.

Thanks