While most Zoom Meetings are scheduled, you don't need to schedule in order to use Zoom Meetings.
To start an instant meeting, open the Zoom app on your computer. On the Home page, click on the orange New Meeting button. An instant meeting using your personal meeting room will be created and you will be joined in.
To invite others to your instant meeting, click on the Participants button in the Zoom Meeting toolbar, then click Invite in the popup that shows.