By default, if you enable a passcode on your Zoom meeting you will need to send meeting participants the passcode through email or include it in your calendar invite.  For meetings scheduled in the Canvas Zoom integration, students can access the passcode using the Invitation button in the Zoom interface.

You can also choose to enable the Embed passcode in invite link for one-click join option.  This will embed the passcode in the join link itself.  If enabled, this setting will allow participants to join by just clicking the link and they will not need to manually enter a passcode.  While this method is more convenient, it is not considered as secure as sending the passcode in a separate communication.  Anyone with access to the link will be able to join the meeting.