The reason Zoom is requiring a passcode or a waiting room is to avoid the so called Zoom bombers who have been joining random meetings by guessing the ID numbers of meetings.
Instructions for the host:
1. If you have already scheduled a meeting that occurs after this change and
a) you already have a waiting room or a passcode in use for the session, you don't need to do anything now.
b) you have not set a passcode nor a waiting room for the meeting, please notice that Zoom will set up a waiting room for that meeting automatically. When you have a waiting room in use, the participant will not be able to join the session on their own but you will need to accept them to join.
2. If you add a passcode to an existing meeting, you will need to resend the calendar invites including the passcode.
3. If you add a new meeting with a passcode, Zoom will add the passcode to the meeting URL (= the web address). This means you will not need to send the password separately to the participants, just send them the URL.
For more details, please see Zoom's own article.
Last updated: 30.6.2020