Adding a password when creating a Zoom meeting creates a necessary layer of security around your meeting. With it, only people that have the meeting ID and password can join, and without it, anybody can join.
To add a Password to your Zoom Meeting:
Create your Zoom meeting by selecting the dropdown menu under New Meeting, and select Use My Personal Meeting ID
Click the orange New Meeting icon the create and start your meeting.
From here, the password for the meeting is shown, as well as the URL needed to invite people to the meeting.