It's great to hear that you're going to be running your business with QuickBooks Online. If you have a QBB file, that's a great first step in getting your data migrated into QBO. I'll explain what you'll need in order to convert your data.
You'll have to restore your QBB file in a trial version of QuickBooks Desktop. Doing that will allow you to migrate your QBB file.
Depending on the version of your QBB file, you may have to get in touch with our team and have our Data Services department complete the migration for you.
I hope this helps. If you have any other questions, please don't hesitate to reach out to our tech support team.