How about Splunk's Search Tutorial? They have many good examples with sample data that you can practice upon.
http://docs.splunk.com/Documentation/Splunk/6.1.2/SearchTutorial/WelcometotheSearchTutorial
Splunk has got very good documentation. For each search command they have given scenarios for understanding.
http://docs.splunk.com/Documentation/Splunk/6.1.2/SearchReference/Abstract
http://docs.splunk.com/Documentation/Splunk/6.1.2/AdvancedDev/Searchscripts
http://docs.splunk.com/images/a/a3/Splunk_4.x_cheatsheet.pdf
Also answers.splunk.com has many questions and answers related to search commands.