Any idea where I can find info on creating a cash balance system?

Question

I'm trying to figure out how I can integrate a cash balance system on a website I'm building. For example, if someone puts $15.00 worth of credit their account, on my site, I would like that info stored and made viewable to the user.
As they make purchases or add more money, the balance program would keep track of this and increase decrease.

Answer 1

//Why are you searching info where you are describing it nicely, now write a code that dose Same

Answer 2

Because I'm not sure if I need to be connected to an API for this type of information to be logged. I'm not even sure how to approach coding something like this...