Each user who has been assigned a license in SharePoint Online has the opportunity to provision a OneDrive for Business Site. If you've administered SharePoint Server previously, you'll know that this was known as My Sites (which you'll see reflected in some of the feature naming nomenclature). It is a site collection where explicit permissions are granted to an individual user. To access it, follow these steps:

1. Launch the User Profile Service application from the classic SharePoint admin page.
2. Under People, select Manage User Profiles.
3. In the Find profiles box, enter the name or address of a user to manage and click Find.
4. Hover over the user. When the down arrow appears on the user, click it. Select Manage Personal Site:

5. If you have access to the site, you will be redirected to the user's OneDrive for Business site. If you do not have permissions, you will receive an error stating <user> does not have permissions to access this resource.

If you selected your own site in the previous example, you will have been logged in. However, if you attempted to access another user's OneDrive site and you don't have permissions, the service application will deny you. If you need to manage another user's OneDrive site, you'll need access, which is addressed with the next task.