Hi Tamana,
Please go to Work Items panel and from the drop-down list choose: Add Sub-Project From Template or Add Sub-milestone From Template. Please see the attachment.
Since Clarizen invites you to a free interactive, real-time demonstration of our features, may I suggest you to join one of our webinars ( see the link-> http://www.clarizen.com/resources/online-demo.html#second ) where you can find way more information and ask questions during our Q&A sessions.
Thanks!