In order to add top spin or back spin to your shots you must firstly unlock a club with this ability.

 

Once you have found a suitable club you will be able to add spin to your shots by selecting the golf ball icon that appears on the right hand side of the game screen when you're taking your shot.

 

If you would like to add side spin to your shots then this can be done by using premium Golf Balls.

These unique Golf Balls can be found in prize Chests and can also be purchased from the Golf Clash shop.

 

Addding Spin:

Topspin: the ball will continue traveling/rolling forward farther. 

Backspin: the ball will stop traveling/rolling sooner (and maybe even roll backward a little)