To be honest, Louise, the Performance Thread is more like fishing than anything else.
You just have to let loose then let fly. It was difficult for me at first, but here I am, cavorting among the wild blossoms along with everyone else.
And don't worry about trying to post in the "correct" place. The CD's scene calls are more like general guidelines than exact directions, so we kinda have an idea where we are. If you have something to contribute to the performance in response to anything that has been going on, you can get the ball rolling, juices flowing, (whatever metaphor suits you best here).
So if you're still having difficulty getting into the swing of things, try 1) Letting loose. Start with a blank screen, and then just accept what comes along without trying to direct or guide it in some direction, then 2) Letting Fly. Respond to what comes along with as much humor, freedom, and exhilaration as you can muster; breathe life into the thread and into whatever characters are right there in front of you. And try and remember, its all in fun.