I need vb help

Okay I know that you can go like for example if i put in this code

Dim aa as string
aa = "dxlglthj"
aa = right(aa , 3)


then you would only see dxl, but i want it to do something like were it read from char number one to like 3, like for example i know this is not really a proper vb6.0 code but i want it to do something like this

Dim aa as string
aa = "tfrhkruyg"
aa = (aa, 3-5)

and then the result would be like "hk, so the string aa would now contain hk instead of "tfrhkruyg"