As far as I know, all CCs in your contract are available to any user on your contract (usually just you if it's your own subscription), and available to any tool that uses CCs. It's a long-standing request to be able to assign credits to specific users or tools, but I haven't seen that feature available yet.
To help understand a small part of it, here are some definitions:
Contract - This is what holds the CCs. A contract can have a number of user accounts assigned to it. If you are the contract manager (you are for an individual contract, or you may have a contract manager for a multi-user contract), you can purchase credits and assign entitlements to the user accounts associated with the contract. For example, if the contract has Lighting Analysis for Revit entitlement, the user may need that assigned to their account.
Use manage.autodesk.com to manage the contract and/or individual accounts.
User/Account - On an individual subscription contract, this is essentially the same as a 'contract'. For multi-user contracts, when you go to manage.autodesk.com with your user login, if you are not the contract manager, you won't be able to manage CCs, but you will see your entitlements.
Use accounts.autodesk.com to see your account info, and you'll also see a link to Manage (manage.autodesk.com) on that page if you are a contract manager or have an individual contract/subscription you'll be able to manage all users' entitlements, or you'll see your entitlements for yourself (like Insight or Lighting Analysis for Revit).
