How to Create a UserForm in Excel VBA
To create an Excel UserForm, open the VBA editor (Alt+F11), then Insert > UserForm. A blank form and the toolbox appear. Drag controls (TextBox, Label, ComboBox, CommandButton) onto the form. Rename every control via the Properties window (e.g. txtCustomerName instead of TextBox1) - your future self will thank you when the form grows.
Show the form from a module with frmCustomer.Show. While building, plan tab order, captions and keyboard shortcuts up front - it saves heavy refactoring later.
Sub OpenCustomerForm()
frmCustomer.Show
End Sub
Private Sub UserForm_Initialize()
Me.Caption = "New Customer"
txtCustomerName.SetFocus
End Sub