You are describing accessing a QB Online account, which is cloud-based. That is not a QB Program. It's your client's subscription to a service. You would add them to your QB Accountant Portal so that you can log into their data account.

I recommend you use (and bookmark) this Link:

https://quickbooks.intuit.com/learn-support/us-quickbooks-community/misc/03/community-us

That is the link to the QB Community. Where you are right now is Not the QB Community. You will want to ask and learn from the QB Community.