After you purchase credits, you can then use them just like tokens at an arcade. You can refer to the "Buckets tab for the billing plan in place: 
Within the bucket, you can see how much is charged depending on usage within the "Rate Card section". 
You can see how much is charged in this example:
In this example, you can see how much CPU cores cost in the On and Off stateBilling methods (How billing works, how funding works, how resource usage is calculated for billing purposes, etc.)
Possibly also explaining how to use the CORE and OnApp APIs to handle most of these tasks programmatically. I'm not sure that this is something we have right now, but some businesses may need it. I'm aware of the OnApp WHMCS plugin, so at the very least we might want to create a simple article that explains how to set it up for our implementation.