On first reading, I would suggest this one - this is a W3School tutorial. Remember to read the related chapters included in this tutorial - Soap, Wsdl, etc. - since this textbook, made as a separate one, will not be so valuable. This tutorial is not specifically related to Android, but will give you all the information you need to understand the uses and limitations of this type of architecture, and then structure your project.
In Android, you will encounter specific limitations of mobile phones and tablets: the network may not be available, and often it does not work: in a pipe, in the basement, in any area with poor network coverage. Thus, you will have to take care of this, either by caching data, or in order for the application to work in degraded mode when the network is unavailable. These are just examples, as I do not know your context.
After that, Android is developed in Java, with a specific API that comes on top of regular java.* Packages. These are just tools for implementing the client side. On the server side, depending on whether you manage these services, you can also perform some implementation. If so, it could be Java, PHP, .Net, whatever: one of the goals of the web services architecture is to remain independent of the remote implementation, only taking care of the exchange protocol. But, reading your question, I think that the first two points are more important (or have a higher priority) than the implementation, since they are prerequisites. ( EDIT : In any case, a useful discussion of this question can be found at fooobar.com/questions/670 / .... )