I'll give details about adding a new company, jmullican.
In QuickBooks Online, each company you add will be a separate paid subscription. If you have multiple companies and want to access it under the same login, you can use the same user ID and password on the Sign Up page.
Here's how:
- Go to the QuickBooks pricing page and select the subscription you want.
- In the Create an Intuit account page, click the Sign in link next to Adding a company to an existing account?.

- Enter the Email address (User ID) and Password.
- Fill out all the information about your new company and you’re good to go.
You can also read this article for reference: Create or add another company.
To check more resources for getting started with QuickBooks Online, you can check it out here: Getting Started With QuickBooks Online.
Please feel free to leave a reply if you have any additional questions or other concerns. Thanks.