When you are in the Create Event tab, check the box next to:
"I need a maximum of (choose number) volunteers to help out with this event"
Click on "(choose number)" and a box with "Select" will appear. Click on the down arrow next to it and select the number of volunteers you need.
NOTE: You MUST check the check box or nobody will be able to sign up for your event.
When you have finished setting up your event, click the "Create Event" button. When you see your event on the calendar there will be a red raised hand under the date. When the total number of volunteers needed have signed up a green raised hand will appear under the date.