Free trials are tracked by the free_trial_started_at date which contributes to the trial-to-paid conversion rates and lead tracking. Customers on a free trial will be labelled as leads until they begin paying for their first subscription.
You can also choose to consider customers who have been billed for a subscription and downgraded to a $0 subscription as active. This is an exception where they would still contribute to the Customers and Subscriptions graphs. Learn more about Free customer handling in our Data Settings documentation.