Create MessageBox to promt me to select data in DropBox

[RooSXL]

I am trying to create an excel report that will be gathering information from different files and it will mainly be driven by macros trigerring macros. However there a couple of cells that require some information in order for the macros to pick the right files. How create a macro that will prompt the user to input data in particular? NOTE: Cells have dropboxes in order for the user to only pick valid information. Does anyone know an easy way to do this?

Thanks,