Windows Azure BizTalk Services (WABS) has been released June this year during the TechEd North America. This is a new service in Windows Azure, which is still in preview mode, and offers application integration and B2B capabilities.
Since this is a fairly new technology you will not find many practical articles on how to implement solutions with it or how to's. Other than the MSDN documentation and a few blog posts there is of course the TechNet Wiki. Here you can find on the BizTalk Server Resources on the TechNet Wiki page under Windows Azure BizTalk Services section a few articles. One of the articles is How to use REST in BizTalk Server 2013 to send a message to Windows Azure BizTalk Services (WABS).
This article has been written by Mandi Ohlinger. She is currently a technical-writer at Microsoft for BizTalk Server, Windows Azure BizTalk Services and BizTalk Server on the VM Role. In this article she explains how to send a message to an EDI Agreement or a Bridge hosted in the BizTalk Services Portal. It describes a simple step by step walk through on how to accomplish that. It is a comprehensive easy to follow article.
In case you want to try it out yourself you can provision a Windows Azure BizTalk Service, by following another article under the same section of Windows Azure Service Bus: Provisioning BizTalk Services using the Windows Azure Management Portal and the information found on MSDN How do I Start Using the Windows Azure BizTalk Services SDK.
So go check out all the wonder, and dive in! The Wiki's warm.