Hi,
That's quite a big topic and probably not something I could attempt to discuss fully here. In short a workspace server is often used to run ad-hoc hand-written or generated SAS language code, such as what might be written in the SAS Enterprise Guide code editor, or generated by adding tasks to a SAS Enterprise Guide project. Stored process servers run stored processes which are packages of pre-published SAS code (with other metadata such as parameter/prompt info etc) which can generate output (reports, files, tables etc). Those stored processes can be run from a number of SAS applications, including SAS Enterprise Guide and the Stored Process Web Application amongst others. Now stored processes can also be run on workspace servers, and there are various pros & cons of doing so, and a longer discussion of the topic could go into that (and many other things). The object spawner is responsible for starting workspace servers and stored processes servers on behalf of the applications that need them, and then controlling their life cycle. The object spawner has various configuration and tuning parameters in metadata to control the behaviour. In a multi-machine environment there might be multiple object spawners working in concert to handle the total workload with load balancing, grid etc.
I'm not sure which documents you might have already read and what your role is within the SAS platform. If you are administering the platform I would strongly recommend the SAS Platform Administration: Fast Track course. In addition to getting into the administration details, its starts off with an overview of the architecture and a discussion of the various tiers and server roles and how SAS applications use those based on what the user is doing in the application. It provides an excellent foundation.
If you haven't already read it, then the SAS 9.3 Intelligence Platform: Overview and in particular the Servers in the SAS Intelligence Platform section might help. If you want more detailed information then the SAS 9.3 Intelligence Platform: Application Server Administration Guide would be a good next step especially the Understanding Workspace Servers and Stored Process Servers section. There are also lots of really good conference papers that discuss SAS architecture too.
I hope this helps.
Cheers
Paul