The search box is located on the right under the Application Bar.
Searching Email
From within the email list, the search box allows you to search the current mail folder for specified text. By default the search is done only on Subject and Sender. If you wish to search the body, to, from, cc or subject areas specifically, use the corresponding keyword in conjunction with your search text. Some examples would include:
Searching Contacts
From within the Address Book, the search box allows you to search the current contact list. All contact list searches are performed on all information within the contact list.