Hello Jenny! The winter sowing exchange is just like the seed exchange or the round robin exchange. There is no signing up to it. You just read the different posts when they come out and if you have something to trade for what you want you make the deal with whomever put the post out. The winter sowing forum gets going good early winter and when time for everyone to start the wintersowing! There will be lots of great posts for Sase and trades. YOu will definitely want to get in on wintersowing. I have a yard full of wonderful flowers due to this method of growing plants from seeds!
BTW, welcome to GW. You will want to try to post a list of what you may have in the way of seeds to trade. And if you don't have alot, now is the time to start getting from wildflowers, trees, etc. And put up a wish list as it helps get the things you want!
Any other questions just ask. None are too silly or simple! Someone here will be quite happy to help you out! Melinda