I'm assuming what you actual want to know is how many new discussions (topics) were created in the past month.
For that you click on the > Content > All Aps > Forums and look at the number of topics.
You can get the same information from Metrics in the Admin and picking Forum Topics after choosing your date range.
Both these obviously only show the number of topics created though, they don't cover how many times a member might ask a new question in an existing thread.
... View more