If you have access to a library you will find shelves of books on statistics that answer this question.

And a few minutes sifting through the results of a Google search will turn up several links. I know this because I did it. And since, I suppose, it would be churlish to say this and then end the post, I will give one link: http://www.math.uiuc.edu/~r-ash/Stat/StatLec1-5.pdf. But really ..... this is surely the sort of thing you can (and should) do yourself. Often, you learn more by doing the search yourself than by being given the information on a platter.