What you get
Credits are granted with your plan and reset at the start of each billing period. They do not roll over.
The balance and the period it belongs to are shown under Quotas in the
console.
What draws from it
A minute of a standard computer and three web searches cost about the same, so
a normal chat that searches a few times is a rounding error next to a build that
runs for half an hour.
Indexing a website does not draw from credits. It runs on the model you chose
in your own workspace, so it lands on that provider’s bill like any other
request.