Admission to Disneyland originally entailed a booklet of coupons, which visitors exchanged for a trip on a given ride. The coupons were labeled "A" through "E," with "E" being reserved for the best and most popular rides. (Hence the term "E-Ticket." ) The system was discontinued in 1982 and replaced by a single-admission system whereby one ticket got you unlimited access to the park. In 2007, Disneyland introduced a different kind of E-ticket, an electronic one that people to purchase and print up online.
Go to Disneyland's official website (see Resources, below) and register a new account with them. Registration is free and just takes a few minutes. When you're finished, make sure you are logged in before proceeding.
Click on the "Buy" bar towards the top of the screen. Find the "Tickets" option and click on it, then click on the type of tickets you want. They will be automatically added to your virtual cart.
Click on the "checkout" button towards the top of the screen to proceed to the checkout. You'll be asked to provide credit card information or similar methods of paying for your E-ticket.
Download the PDF of your purchased tickets--there should be one for each E-Ticket you purchased--and open them using Adobe Acrobat. Print them out using your printer, making sure each of the E-tickets is complete.
Go directly to the turnstiles when you arrive at Disneyland. You don't need to wait in line at the ticket counters or the will call booths. The ticket checker will scan the bar code on your E-tickets and grant you immediate access to the park.