The essence of Design patterns in Java

Helo guys, am currently taking a course titled 'Data Structure And Algorithm' and the first topic we looked at is design patterns using java where we discussed the container pattern,iterator pattern, visitor pattern e.t.c and they all seemed abstract to me even though i have a good understanding of java basics. so i will like to know what design pattern is all about i.e the motivation behind it and how it is related to the above mentioned course.Thanks