Start an event and check clients in

From your 'My Hub' page (please see below)

On the left hand side of your account, you will see the side menu where you can select 'Calendar'.

This will show you an overview of that month's sessions/events

Here you can click on the event followed by the arrow to 'View'

If you hit the 'Start Event' button at the bottom of your screen

You will be able to take a register and check all attendees in.