How to have coins in my project?

Hello, I will not write entire leaderstats script here but I can give you helpful tutorial, its fairly simple and it will help you add custom values on your game

https://www.youtube.com/watch?v=2fX5DRjLMuQ&ab_channel=TheDevKing

Try watching this, he explains leaderstats concept easily.

if you do not understand this then I suggest you watch earlier tutorials from him or different players so they will explain everything from start before you start getting to this point.