The idea is that you make a three word phrase or sentence using the last three letters of the previous post as the initial letters of your phrase. If that sounds a bit confusing, here's an example:
1) Rhubarb and custard .... last three letters are a-r-d, so... 2) A Red Delicious! ... last three letters are o-u-s... 3) Olive's unusually suntanned
And so on.
So let's start with the last three letters of #3 above: