SuiteCRM Reports and Charts

I have been to create chart for Leads grouped by lead source , but am getting weird chart.

I am confused on how can I create a good chart.

Also what does below parameters in Conditions tab does is confusing.

  1. Function
    2)Group Format Option
    3)Total
    4)MainGroup (on top under Condition tab)

Can you please help me understand these and when can they be used.

Also some good example on setting up a chart.