Jmeter :Sampler Vs PreProcessor Vs Post Processor Vs Function

Jmeter : Sampler Vs PreProcessor Vs Post Processor Vs Function

JMeter provides following components:

• Sampler – a standalone Sampler
• PreProcessor – a Pre Processor to another Sampler which is executed before Sampler and can be used for pre-requisites setup, i.e. to generate some input 
• PostProcessor –  a Post Processor which is executed after Sampler and can be used for recovery or clean up
• Assertion – an advanced Assertion with full access to JMeter API .Java conditional logic can be used to set assertion result
• __Beanshell function – a JMeter Function which allows  the execution of custom Beanshell code during a Sampler run

Refer For More Details : 

http://blazemeter.com/blog/queen-jmeters-built-componentshow-use-beanshell