Each category of metrics has its own button. This is the button for the CPU metric category. Click on it to display the CPU metrics available for threshold monitoring. Each metric category presents its choices in a similar manner.

A metric category button looks like this when it is selected. The LED on the button shows bright green.

A metric category button looks like this when it is no longer selected, but metrics within that category are selected.

A metric category button looks like this when both the category and the metrics within that category are selected.

When this button is on, the display work area is shown.

When this button is on, the threshold work area is shown.

This button (more...Advanced) is active only when the threshold work area is shown.

Click on this button to start the session currently specified. The displays and thresholds you have selected become active as soon as you click on this button. This button is active only when no session is running.
More information on sessions.

Click on this button to stop the current session. All metric displays close. This button is active only when a session is running.