From the main homepage of Tabroom, you can access a variety of tournament calendars.
The main Tabroom homepage shows a list of all upcoming tournaments:
Clicking the name of any tournament will take you to that tournaments information page, where you can view the invitation, contact info, etc. Clicking the name of a circuit in the tournament list will take you to a sub-calendar showing just tournaments from that circuit.
Or, you can filter the list of tournaments by date, country, or state using the tools on the right.
On Tabroom, a "Circuit" is a collection of related tournaments, for example from a specific league or state. All tournaments must belong to at least one circuit. Each Circuit has it's own sub-calendar.
From the home page, click the "Circuits" tab:
This will show you a list of all available circuits on Tabroom.
Select a circuit, and you will be taken to that circuits sub-calendar: