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)