Normally, you need to have tickets (free) to attend the weekly Papal Audience held almost every Wednesday in Rome. There is an exception for the entire month of August every year, when no tickets are issued. Therefore you DO NOT NEED a ticket to attend the audience.
It is suggested that you just go to the audience early. It will probably be in the Paul VI Audience Hall at 9.30 or 10 AM. But you should plan to get there by 7 AM and stand in line. You will have free access.
For this year, tickets will be issued beginning in September, with the exception of Sept 13, 2017, when the Pope will be visiting Colombia.