I use a user form in which the user shall enter a date in a text field. I
then have a sub that checks if the date is valid. If not so I show a message
box. However I want the program to show the message box and when the user
clicks OK I want the user form to still be shown.

Private Sub checkDate()
If (Not (IsDate(userForm1.TextBox1.Text))) Then
MsgBox ("Date not valid")
End If
If (Not (IsDate(userForm1.TextBox2.Text))) Then
MsgBox ("Date not valid")
Else: Call mainProgram
End If
End Sub

The problem is that I do not know how to write a sub that just shows the
user form.
Now I just have a sub that gives instructions when the user clicks a button
on the user form. This sub calls checkDate as you can see below.

Private Sub genereraRapportKnapp_Click()
Call checkDate
Call mainProgram
Unload Me
End Sub

The user form is created in a Modul when pressing a button.

Public Sub startKnapp_Click()
userForm1.Show
End Sub

If anyone has a clue how to solve this please help me, I seem to be quite
lost....Thank you.