Query on Excel macro - Asking a value in macr

Hello,
I would like to know how to write a macro that should ask in during the run, a particular value and than consider that value in its run downstream.
Everytime when I run that macro It should ask me to reenter that value and it should come a a popper, once given the value and clicked ok, it should use that value and run the rest of the macro.
Please help
Regards
Sunil