Get_customer() logic

I dont understand the logic of below…could someone give 2 examples and explain how to define a period? I am still not sure I get it after I checked all the related questions posts…
For example, from 4/30/2012 to 5/2/2012 consider as one period, but it only has 2 days? or we do 4/30/2012-6/2/2012?

Thank you in advance!!

‘‘More concretely, given a month ym (from yearmonth in churn ), we’ll count the number of subscriptions where start_date comes before the first day of ym , and where end_date is after the last day of the previous month (which is to say that the end_date is greater than or equal to the first day of ym ).’’

Hi @candiceliu93:

please provide a question link according to these guidelines to aid us in answering your query.

Thanks

Please see the screen link: https://app.dataquest.io/m/468/business-metrics/8/churn-rate

Ok. Looks like I haven’t attempted it yet so I’ll open it for others to answer.