Cast Member discounted tickets and annual passes can be purchased in one of two ways. The first, as the PP mentioned, is at Company D locations around property. This is also the only place that you can purchase discounted tickets for special events like Night of Joy, Mickey's Not So Scary Halloween Party, and Mickey's Very Merry Christmas Party.
You can also call Cast Member Ticket Services (Number is found on the HUB) and purchase over the phone. Tickets would then be picked up at Guest Relations, Resort Concierge, or Will Call at the Parks.
The current discount is 10% and you are limited to purchasing 15 per day. However, the discounting does not apply to Florida Resident Tickets or Florida Resident Annual Passes. The pricing can be found on the HUB under the "Complimentary Admission" Tab.
Keep in mind, all of this is subject to change without notice.