In addition to the apps that come with iPad and that you use with > Apps > Contacts.
Tap Accounts > Add Account.
Do one of the following:
Tap a service—for example, iCloud or Microsoft Exchange—then enter your account information.
Tap Other, tap Add LDAP Account or Add CardDAV Account (if your organization supports it), then enter the server and account information.
See Set up Exchange ActiveSync on your iPhone or iPad.
If you turn on iCloud Keychain on your iPad, your accounts stay up to date on all your devices that have iCloud Keychain turned on. See Use iCloud on iPad