How to make a Password input prompt window for Excel and mask the input so that you can't see what is being typed into the window.
This tutorial also shows you how to:
This tutorial is made for beginners, and, though it requires using a little bit of VBA and creating a UserForm, the entire process is shown in an easy-to-follow manner from start to finish.
Require a Password to View Hidden Worksheets in Excel
Masking Password Input (microsoft resource)
UserForm PasswordChar Property (microsoft resource)
Follow along with the tutorial by downloading the files used in it. (Completely Free)