When you go to the main Disney World site, there is an option along the top under "Where to Eat" to make dining reservations (there's the same link under "My Reservations" as well, or at least a similar link). Clicking on that will take you to the dining reservation system.
When you search for a date that is greater than 180 days out, you will then be prompted to confirm your resort reservation. This is where you'll enter your resort confirmation number (and some other info) to open up the 180+10. Note that (at this time, it may change in the near future) that CRT and the dinner shows will require a couple of extra steps as they are not on the current system.
For those "special" reservations, they will show in the list with text denoting that there "may be" availability and a link. This like takes you to the specific restaurant reservation search (which is the "old" system, replaced earlier this year). Here you will again need to confirm your resort reservation via a link on that page, and then search again with the tools in the page.
For a detailed walkthrough, I have a tutorial down in my signature below.