To Workflow guides, use the links provided below.
Download Workflow Developer's Guide: (HTML version): http://download.oracle.com/docs/cd/B19306_01/workflow.102/b15853/toc.htm
PDF version: http://download.oracle.com/docs/cd/B14099_19/integrate.1012/b12161.pdf
Workflow API Guide: http://download.oracle.com/docs/cd/B14099_19/integrate.1012/b12163.pdf
Workflow System Administrator Guide: http://download.oracle.com/docs/cd/B19306_01/workflow.102/b15852.pdf