Microsoft Excel Spreadsheet  Training

What is a UserForm? 

Create User Form in Excel - Step 1 of 3

What is a  user form in Excel VBA?
Forms are objects in Excel that help us to enter data quickly and easily. To create a custom dialog box in Excel, you must create a UserForm. To create a UserForm, click UserForm on the Insert menu in the Visual Basic Editor.The Excel training video describes how this is a straightforward one click step.
Use the Properties window to change the name, behavior, and appearance of the form. For example, to change the caption on a form, set the Caption property.

Further reading on Userforms

Create user form using macro in Excel