Part 3 of the workshop examines the different aspects of an execution plan, from cardinality estimates to parallel execution and explains what information you should be gleaming from the plan and how it affects the execution. It offers insight into what caused the Optimizer to make the decision it did as well as a set of corrective measures that can be used to improve each aspect of the plan.
More information on displaying and reading execution plans can be found in my previous blog posts on DBMS_XPLAN.DISPLAY_CURSOR and using SQL Monitor. Or in the white paper Explain the Explain Plan.