Free dining is usually offered in April for reservations in late August through September. You must pay full price for the room and purchase at least a one day MYW ticket for everyone in the room. Free dining will probably be the basic
DDP, which includes one counter service meal, one table service meal, and one snack /day/person. Tips are not included.
There have also been times when Disney has offered the Bounce Back dining for people who are there in Sept-Dec, where they can book a trip for the next late August-Sept and get free dining for that trip. Disney is currently sending out PIN codes for free dining to certain people, but those are random and can only be used by the people they are sent out to. Unfortunately, there doesn't seem to be any rhyme or reason who gets PIN Codes. I know I've signed up for everything I can think of and order that silly planning DVD every year and have still never gotten a PIN.
Again usually free dining is only for late August-Sept, but Disney did offer free dining last year for certain dates in Oct, Nov, and Dec. It has never been offered for June trips though. With all the kids out of school it's never been necessary for Disney.
Oh yes, free dining is usually offered first to Disney VISA card holders then about a week later to the general public. Rooms may be limited. Keep a watch here on the DIS over on the Resorts/Codes Board. As the time gets closer for it to be announced, you'll see all kinds of threads about it.