Mean vs think

[M3dic]

Hi,
in my language these two words mean the same. I understand where to use these words but I am not able to explain it to my friend? does it have a rule?

just to be sure:
guy a: I think that the girl over there is pretty.
guy b: Do you mean the left one?
right?

I'm really sorry but in our language these two words have got really the same meaning.

Does it have a rule where to use it or in English it mean two different words and there is no doubt where to use mean and where think?

Thank you very much

[Haihao]

[M3dic]

thank you very much