If you are an Admin or Global Admin you will be able to access the Billing page by using the dropdown in the left-hand navigation by selecting 'Billing'.
Track your Billing Progress in a Doc-based Plan
If you are on a Doc-based pricing plan, you can track your active Docs usage by calendar month along with a list of all the Docs in that month below the graph.
The graph and Docs list are auto-filtered by the current month. You can click on any of the other months to change the view.
Click on the title of any Doc to view the Doc itself, or the link on the right-hand side to view the Doc analytics.
The data is refreshed on daily basis.