Does anyone know how to use 'Charge Fun'?

The first picture is pressing 'Charge Fun', then opening it to see if it's charging (PS: because you can get gems). The second picture, look at the part I circled↓ You can watch an ad to get 100 blue gems. For the second ad, you need to be quick (you get a total of 200 blue gems). And as you can see the long press I marked, you get as much as you charge... but you don't need to press slowly, just long press the lightning icon directly to get gems (meaning you get gems for each time you charge).