Your credit balance is always visible:
In the header next to your profile (shows coin icon with number)
On the Generate button (shows cost and current balance)
For more details:
Click on your profile
Select Profile from the menu
View your complete credit information
You can see:
Total Available: Credits ready to use
Regular Credits: From your subscription
After generating a video:
Balance updates immediately
Cost is deducted right away
Check My Videos for confirmation