From July 1955 until October 1955 you would buy tickets for each ride i.e. Mr Toad, Pack Mules etc.
Lettered ticket books were used from October 1955 until around 1982.
October 1955 to June 1956 tickets were A-C. July 1956 to 1959 were A-D and E ticket was introduced in 1959.
Between 1980-1982 they had both ticket books or you could buy a "Passport" The passport was a cardboard ticket that you would wear and when you went on a ride instead of giving them a ticket you would show your "Passport".
After 1982 once the ticket books were phased out you no longer had to show your "Passport" to the ride operators but you did need to have your multiday "Passport" stamped each day you entered the park.
Here is an example of one from 1993:
A piece of trivia: The ticket books are still valid ..if you present a ticket from an old ticket book to the ticket booth at Disneyland they will give you face value (A Ticket was 10 cents and E ticket was 50 cents) as a discount for entrance to the park..