How do I see my API usage?

The plan I subscribed to has a limited amount of calls per API. How can I monitor my usage against that?

The numbers of requests, for different APIs, that your application has made are shown on your application page.

Click 'Apps' in the main menu and then click on your application. Under 'Subscribed Plans' you will see all plans your application is subscribed to. 

For each API contained in that plan you can see the usage compared to the rate limit of the plan.