Select from Open Excel Workbooks

I am new to this development community, so please show me some grace here.

I would like to create a dialogue that allows the user to select which currently open Excel workbook to run further code on. For example, if I have three opened instances of Excel on my Desktop, I would like to scan for the filenames of these opened documents, and then have the list of filenames populate a dropdown dialogue from which the user can select. Then, the subsequent operations will only be performed on the selected workbook.