How do you make a buy and equip system

I am completely lost and have no idea where start, begin or even create something like this. Please help me by giving me tips and pieces of code that can point me in the right direction.

I am making a game that you tap to earn cash that I put under a variable value called money, I have made the getting and collecting money system down and completed. Now I need something for the user to do with that money. What I need is a UI store system that the player will be able to go through to spend their money in a different scene that you can access from the Home screen and the End Screen. These objects that the user can buy are power ups. For example a power up I was think about was increasing the number of taps the user clicks by 5 every 20 taps the user gets. I will need to make multiple of these power ups that the user can buy then the UI will give an option to equip this power up but if the user already has a existing power up equipped that it will unequip the previous item. I also need something to prevent a purchase from going on if the player does not have enough money. Finally I need a script that will subtract the amount of money that user used to buy the power up and save the value as the new money value.

Extra details

The variable that holds the tap value is called counter.

The variable money holds the currency value earned by the player.