The history shows all the changes that have been made to the customer subscription. You can find here information on when an offer has been started and when it was ended.

This is an example of a monthly subscription.

The customer started the subscription on the 15th of October 2019 (subscribed) and enjoyed a 14 days free trial until the 29th of October 2019. As the customer hasn't cancelled before the trial ended the subscription continued automatically and renewed itself with 30 days on the 30th of October 2019. 

Here is another example.

This customer subscribed on the 6th of October 2018 to an offer that included a 7 days trial. After the trial ended the system tried to automatically renew the offer by 30 days but the transaction failed. In these cases, our system will retry the transaction three times and then downgrade the account.