Now I have a question. What is the Waterfall?
It's a Classical Life Cycle of a Program.....Often called the Classical Life Cycle Or Linear Sequential Model......Bacasically these are steps or guidelines to be followed from the very Begning of Proposeing a new system and following it until it remains in use.........This is called a Waterfall because like Waterfall the Steps are one way down you start at the top and go down the ladder without coming back ( well theoricatically...but in real you have to come back )

Steps are
  • Analysis -- What factor ...Establishing What is the Problem(Until you have properly Identified the Problem you cannot find a solution)....Why we need to this
  • Design -- Logical Design ... The How factor .....mostly done on paper..how are we going to Correct the problem
  • Coding -- implementing What we have done in the above two phases
  • testing -- Preparing various test Case Plans ....and putting the moduses and the product as a whole through it
  • implementation/Mantainance --Preparing Implementating Plan ..deployig it at the site and mantaining the product till it is in service

You start from the First Process that is Analysis and when you complete Analysis you go down to the next process that is design.......theroacially it sounds very good ...Complete one process and go down but most of the time dosen't work......new things creep up , requirements change.......market changes or just because the USer was shy was not pass what actually he wants in the system ........ you have to accomodate changes that why Irtrative Process models are more fesible these days as compared to Classical Life Cycle or Waterfall Model Model .

For Further explanation.....i would recommend you try giving Software Engineering A Practitioner's Approch By Roger S Pressman a Look ...

--Good Luck--