where do I go to use my coins to buy boosters?
Select the clubs button at the bottom left corner, right beside the red star leader board.
There you will see the “gem rewards” button
You need gems, not coins to buy boosters in the club shop
You can buy boosters for 6,000 coins when you play a hand. If you click the + at the bottom of the booster needed, you’ll get a pop-up asking if you want to spend 6,000 coins for one.