To use your ball effect on PC:
When in any game select the blue wand icon at the top of the screen to the right of the INVITES button. Select the ball effect you would like to use and SAVE. You can also turn off your ball effect at any time by selecting the wand again and choosing NONE.
To use your ball effect on Mobile:
When in any game select the ball icon in the bottom right like you were going to apply spin to your ball. Above the spin menu is the new ball effects menu. Here you can choose or purchase any ball effect. Select the one you want and close the box. This will apply the ball effect. You can also remove the ball effect at any time by going into the same menu and choosing the red circle with a line through it.