Sorry, also the given link leads to BPEL how-tos, I did not completely replied to your question. :(
I just gave an eye of the link above, and there is no complete tutorial that explains the creation of a HelloWorld process.
I had started it (http://doc.petalslink.com/display/petalsstudiosnapshot/Creating+a+HelloWorld+process) few months ago, and I was stopped by a technical problem.
The tutorial is a flash demo, made with Wink for another occasion. I wanted to reuse it and share it on a video site (like Vimeo or Youtube, for bandwidth and referencement reasons), but SWF is not supported by any them.
Therefore, I will have to find time to redo this demo and capture it under a video format.
I will try to do it this week.
Until then, you can try by yourself with the information the wiki provides. :)
If you know the basics of the BPEL language, I think it should not be too hard.
Right now, our schedule does not allow us to work on tutorials.
The current roadmap will be complete in about 4 weeks. The next one should normally include a full review of our tutorials. That may be the occasion of putting a full BPEL scenario in the loop.