speak and talk

my name is vinko. I come from Slovenia. I don´t now when we use speak and when we use talk. I need this explanation, because I must this explain my class. I need at liest two group of word, which we often exchange ( for example watch/look).

[Tdol]

Try this exercise on the two verbs, which will give you some examples of their usage.
http://www.usingenglish.com/handouts/366.html