Besides entering contacts, you can:
Use your iCloud contacts: Go to Settings > iCloud, then turn on Contacts.
Import your Facebook Friends: Go to Settings > Facebook, then turn on Contacts in the “Allow These Apps to Use Your Accounts” list. This creates a Facebook group in Contacts.
Use your Google contacts: Go to Settings > Mail, Contacts, Calendars, then tap your Google account and turn on Contacts.
Access a Microsoft Exchange Global Address List: Go to Settings > Mail, Contacts, Calendars, then tap your Exchange account and turn on Contacts.
Set up an LDAP or CardDAV account to access business or school directories: Go to Settings > Mail, Contacts, Calendars > Add Account > Other. Then tap “Add LDAP Account” or “Add CardDAV Account” and enter the account information.
Sync contacts from your computer, Yahoo!, or Google: In iTunes on your computer, turn on contact syncing in the device info pane. For information, see iTunes Help.
Import contacts from a vCard: Tap a .vcf attachment in an email or message.
Search a directory. Tap Groups, tap the GAL, CardDAV, or LDAP directory you want to search, then enter your search. To save the info to your contacts, tap Add Contact.
Show or hide a group. Tap Groups, then select the groups you want to see. This button appears only if you have more than one source of contacts.
Update your contacts with Twitter. Go to Settings > Twitter, then tap Update Contacts. Twitter matches email addresses and phone numbers in order to add Twitter user names and photos to your contact cards.
When you have contacts from multiple sources, you might have multiple entries for the same person. To keep redundant contacts from appearing in your All Contacts list, contacts from different sources that have the same name are linked and displayed as a single unified contact. When you view a unified contact, the title Unified Info appears.
Unify contacts. If two entries for the same person aren’t linked automatically, you can unify them manually. Edit one of the contacts, tap Edit, then tap Link Contact and choose the other contact entry to link to.
Linked contacts aren’t merged. If you change or add information in a unified contact, the changes are copied to each source account where that information already exists.
If you link contacts with different first or last names, the names on the individual cards won’t change, but only one name appears on the unified card. To choose which name appears when you view the unified card, tap Edit, tap the linked card with the name you prefer, then tap Use This Name For Unified Card.