Perhaps someone could explain this forum jam to me... It sounds interesting
Basically, someone (TBC) will provide a backing track for you to play along with. You'll need some sort of recording device to record your solo, then you'll need to convert it to mp3 and e-mail it to whoever's on mixing and mastering duties (also TBC). They'll produce a final track with all the contributors' solos and post it on the forum for our listening pleasure.
If you don't already have a software recording gadget, I recommend Audacity- it's free to download and easy to find with a google search.