For WDW:
Solo entrance: Your Cast ID serves as your "Ticket," just walk through any turnstile and put your ID in the slot as if it were a ticket. The same goes for getting fastpasses while in the park. If your Cast ID does not have a photo on it, bring a photo ID just in case there is an issue.
Gettin in Friends and family: You will need your MainGate, Cast ID, and Photo ID (Drivers License or Passport) if Cast ID does not have a photo. Got to the turnstiles that have the sign "Cast Member Entrance and Disney'e Electronic Ticket." Present your cards to the host or hostess and they will guide you from there. Each member you get in will receive their own paper ticket and have their fingerprint attached to the ticket for re-admission if park hopping that day.