What is really the Builder pattern?

This question has already been asked, I read many articles about this pattern but I found two ways of doing it, for me they are two different patterns. For example in this post. The first answer (JoshBerke : do a lot of things to build an object) and the second answer (Aaron Ferguson : solution to Telescoping Constructor Pattern ans immutable objects with some optional parameters) are completely different, what is really the Builder pattern and when to use it ? Thanks for helping.