I’ve received several questions lately about managing contacts and email lists in Google Apps, and rather than reinvent the wheel by creating my own set of instructions, I’ve decided to link to this very detailed set of instructions created by Google.
http://edutraining.googleapps.com/Training-Home/module-2-mail/module-2-chapter-3
These instructions walk you through the process of adding/deleting contacts, uploading existing contacts, creating email groups of parents, students, colleagues, etc., and sending mail to contacts and contact lists.