Hi WSplawn, welcome to the forum.

You can use the Workbook_Open event to do this. In the VB Editor (ALT+F11) double-click on the ThisWorkbook module and then put the following code in the window to the right:
Private Sub Workbook_Open()
UserForm1.Show
End Sub
Close the VB Editor and save your workbook. Change "UserForm1" to the name of your user form, of course.