In the SQL Window and in the Debugger's Test Window you can use the Statistics page to view the resources used by the last executed SQL statement or program unit. This information can be a big help when optimizing your SQL or PL/SQL code. Make a change, re-execute it, and view the statistics to determine the effects.
The screenshot above is an example of the statistics you may expect. You can use a preference setting to add any statistic that Oracle provides. The statistics that are available depend on the version of the Oracle Server you are using.